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<body style="display: inherit; "><div class="head"><p></p><h1 class="title" id="title">JSON-LD Syntax 1.0</h1><h2 id="subtitle">A Context-based JSON Serialization for Linking Data</h2><h2 id="unofficial-draft-24-october-2011">Unofficial Draft 24 October 2011</h2><dl><dt>Editor:</dt><dd><a href="http://manu.sporny.org/">Manu Sporny</a>, <a href="http://digitalbazaar.com/">Digital Bazaar</a></dd>
<dt>Authors:</dt><dd><a href="http://digitalbazaar.com/">Manu Sporny</a>, <a href="http://digitalbazaar.com/">Digital Bazaar</a></dd>
<dd><a href="http://digitalbazaar.com/">Dave Longley</a>, <a href="http://digitalbazaar.com/">Digital Bazaar</a></dd>
<dd><a href="http://greggkellogg.net/">Gregg Kellogg</a>, <a href="http://kellogg-assoc.com/">Kellogg Associates</a></dd>
<dd><a href="http://www.markus-lanthaler.com/">Markus Lanthaler</a>, <a href="http://www.tugraz.at/">Graz University of Technology</a></dd>
<dd><a href="http://webbackplane.com/">Mark Birbeck</a>, <a href="http://webbackplane.com/">Backplane Ltd.</a></dd>
</dl><p>This document is also available in this non-normative format: <a href="diff-20111016.html">diff to previous version</a>.</p><p class="copyright">This document is licensed under a <a class="subfoot" href="http://creativecommons.org/licenses/by/3.0/" rel="license">Creative Commons Attribution 3.0 License</a>.</p><hr /></div>
<div id="abstract" class="introductory section"><h2>Abstract</h2>
<p>
JSON [<cite><a class="bibref" rel="biblioentry" href="#bib-RFC4627">RFC4627</a></cite>] has proven to be a highly useful object serialization and
messaging format. In an attempt to harmonize the representation of <a class="tref internalDFN" title="linked_data" href="#dfn-linked_data">Linked Data</a>
in JSON, this specification outlines a common JSON representation format for
expressing directed graphs; mixing both Linked Data and non-Linked Data in
a single document.
</p>
</div><div id="sotd" class="introductory section"><h2>Status of This Document</h2><p>This document is merely a public working draft of a potential specification. It has no official standing of any kind and does not represent the support or consensus of any standards organisation.</p>
<p>This document is an experimental work in progress.</p>

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</div><div id="toc" class="section"><h2 class="introductory">Table of Contents</h2><ul class="toc"><li class="tocline"><a href="#introduction" class="tocxref"><span class="secno">1. </span>Introduction</a><ul class="toc"><li class="tocline"><a href="#how-to-read-this-document" class="tocxref"><span class="secno">1.1 </span>How to Read this Document</a></li><li class="tocline"><a href="#syntax-tokens-and-keywords" class="tocxref"><span class="secno">1.2 </span>Syntax Tokens and Keywords</a></li><li class="tocline"><a href="#contributing" class="tocxref"><span class="secno">1.3 </span>Contributing</a></li></ul></li><li class="tocline"><a href="#design" class="tocxref"><span class="secno">2. </span>Design</a><ul class="toc"><li class="tocline"><a href="#goals-and-rationale" class="tocxref"><span class="secno">2.1 </span>Goals and Rationale</a></li><li class="tocline"><a href="#linked-data" class="tocxref"><span class="secno">2.2 </span>Linked Data</a></li><li class="tocline"><a href="#linking-data" class="tocxref"><span class="secno">2.3 </span>Linking Data</a></li><li class="tocline"><a href="#the-context" class="tocxref"><span class="secno">2.4 </span>The Context</a><ul class="toc"><li class="tocline"><a href="#external-contexts" class="tocxref"><span class="secno">2.4.1 </span>External Contexts</a></li></ul></li><li class="tocline"><a href="#from-json-to-json-ld" class="tocxref"><span class="secno">2.5 </span>From JSON to JSON-LD</a></li></ul></li><li class="tocline"><a href="#basic-concepts" class="tocxref"><span class="secno">3. </span>Basic Concepts</a><ul class="toc"><li class="tocline"><a href="#iris" class="tocxref"><span class="secno">3.1 </span>IRIs</a></li><li class="tocline"><a href="#identifying-the-subject" class="tocxref"><span class="secno">3.2 </span>Identifying the Subject</a></li><li class="tocline"><a href="#specifying-the-type" class="tocxref"><span class="secno">3.3 </span>Specifying the Type</a></li><li class="tocline"><a href="#strings" class="tocxref"><span class="secno">3.4 </span>Strings</a></li><li class="tocline"><a href="#string-internationalization" class="tocxref"><span class="secno">3.5 </span>String Internationalization</a></li><li class="tocline"><a href="#typed-literals" class="tocxref"><span class="secno">3.6 </span>Typed Literals</a></li><li class="tocline"><a href="#multiple-objects-for-a-single-property" class="tocxref"><span class="secno">3.7 </span>Multiple Objects for a Single Property</a></li><li class="tocline"><a href="#multiple-typed-literals-for-a-single-property" class="tocxref"><span class="secno">3.8 </span>Multiple Typed Literals for a Single Property</a></li><li class="tocline"><a href="#lists" class="tocxref"><span class="secno">3.9 </span>Lists</a></li></ul></li><li class="tocline"><a href="#advanced-concepts" class="tocxref"><span class="secno">4. </span>Advanced Concepts</a><ul class="toc"><li class="tocline"><a href="#base-uri" class="tocxref"><span class="secno">4.1 </span>Base URI</a></li><li class="tocline"><a href="#default-vocabulary" class="tocxref"><span class="secno">4.2 </span>Default Vocabulary</a></li><li class="tocline"><a href="#default-language" class="tocxref"><span class="secno">4.3 </span>Default Language</a></li><li class="tocline"><a href="#vocabulary-prefixes" class="tocxref"><span class="secno">4.4 </span>Vocabulary Prefixes</a></li><li class="tocline"><a href="#automatic-typing" class="tocxref"><span class="secno">4.5 </span>Automatic Typing</a></li><li class="tocline"><a href="#type-coercion" class="tocxref"><span class="secno">4.6 </span>Type Coercion</a></li><li class="tocline"><a href="#chaining" class="tocxref"><span class="secno">4.7 </span>Chaining</a></li><li class="tocline"><a href="#identifying-unlabeled-nodes" class="tocxref"><span class="secno">4.8 </span>Identifying Unlabeled Nodes</a></li><li class="tocline"><a href="#aliasing-keywords" class="tocxref"><span class="secno">4.9 </span>Aliasing Keywords</a></li></ul></li><li class="tocline"><a href="#using-json-ld-for-rdf" class="tocxref"><span class="secno">5. </span>Using JSON-LD for RDF</a></li><li class="tocline"><a href="#markup-examples" class="tocxref"><span class="secno">A. </span>Markup Examples</a><ul class="toc"><li class="tocline"><a href="#turtle" class="tocxref"><span class="secno">A.1 </span>Turtle</a><ul class="toc"><li class="tocline"><a href="#prefix-and-base-definitions" class="tocxref"><span class="secno">A.1.1 </span>Prefix and Base definitions</a></li><li class="tocline"><a href="#chaining-1" class="tocxref"><span class="secno">A.1.2 </span>Chaining</a></li><li class="tocline"><a href="#lists-1" class="tocxref"><span class="secno">A.1.3 </span>Lists</a></li></ul></li><li class="tocline"><a href="#rdfa" class="tocxref"><span class="secno">A.2 </span>RDFa</a></li><li class="tocline"><a href="#microformats" class="tocxref"><span class="secno">A.3 </span>Microformats</a></li><li class="tocline"><a href="#microdata" class="tocxref"><span class="secno">A.4 </span>Microdata</a></li></ul></li><li class="tocline"><a href="#mashing-up-vocabularies" class="tocxref"><span class="secno">B. </span>Mashing Up Vocabularies</a></li><li class="tocline"><a href="#iana-considerations" class="tocxref"><span class="secno">C. </span>IANA Considerations</a></li><li class="tocline"><a href="#acknowledgements" class="tocxref"><span class="secno">D. </span>Acknowledgements</a></li><li class="tocline"><a href="#references" class="tocxref"><span class="secno">E. </span>References</a><ul class="toc"><li class="tocline"><a href="#normative-references" class="tocxref"><span class="secno">E.1 </span>Normative references</a></li><li class="tocline"><a href="#informative-references" class="tocxref"><span class="secno">E.2 </span>Informative references</a></li></ul></li></ul></div>



<div id="introduction" class="section">

<!-- OddPage -->
<h2><span class="secno">1. </span>Introduction</h2>

<p>
JSON, as specified in [<cite><a class="bibref" rel="biblioentry" href="#bib-RFC4627">RFC4627</a></cite>], is a simple language for representing
data on the Web. <a class="tref internalDFN" title="linked_data" href="#dfn-linked_data">Linked Data</a> is a technique for creating a graph of interlinked data across
different
documents or Web sites. Data entities are described using <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>s,
which are typically dereferencable and thus may be used to find more
information about an entity, creating a &quot;Web of Knowledge&quot;. JSON-LD is intended to be a simple
publishing method for expressing not only Linked Data in JSON, but also for adding
semantics to existing JSON.
</p>

<p>
JSON-LD is designed as a light-weight syntax that can be used to express
<a class="tref internalDFN" title="linked_data" href="#dfn-linked_data">Linked Data</a>. It is primarily intended to be a way to use Linked Data
in Javascript and other Web-based programming environments. It is also
useful when building interoperable Web services and when storing Linked
Data in JSON-based document storage engines. It is practical and designed
to be as simple as possible, utilizing the large number of JSON parsers
and libraries available today. It is designed to be able to
express key-value pairs, RDF data, RDFa [<cite><a class="bibref" rel="biblioentry" href="#bib-RDFA-CORE">RDFA-CORE</a></cite>] data, Microformats
[<cite><a class="bibref" rel="biblioentry" href="#bib-MICROFORMATS">MICROFORMATS</a></cite>] data, and Microdata [<cite><a class="bibref" rel="biblioentry" href="#bib-MICRODATA">MICRODATA</a></cite>]. That is, it supports
every major Web-based structured data model in use today.
</p>

<p>
The syntax does not necessarily require applications to change their JSON, but
allows to easily add meaning by adding context in a way that is either in-band or
out-of-band. The syntax is designed to not disturb already deployed systems
running on JSON, but provide a smooth upgrade path from JSON to JSON with
added semantics. Finally, the format is intended to be easy to parse, efficient to
generate, convertible to RDF in one pass, and require a very small memory footprint
in order to operate.
</p>

<div id="how-to-read-this-document" class="section">
<h3><span class="secno">1.1 </span>How to Read this Document</h3>

<p>
This document is a detailed specification for a serialization of Linked
Data in JSON. The document is primarily intended for the following audiences:
</p>

<ul>
  <li>Web developers that want to understand the design decisions and
  language syntax for JSON-LD.</li>
  <li>Software developers that want to encode Microformats, RDFa, or Microdata
  in a way that is cross-language compatible via JSON.</li>
  <li>Software developers that want to implement processors and APIs for
  JSON-LD.</li>
</ul>

<p>This specification does not describe the processing algorithms and programming interfaces,
  for those see [<cite><a class="bibref" rel="biblioentry" href="#bib-JSON-LD-API">JSON-LD-API</a></cite>].</p>

<p>
To understand the basics in this specification you must first be familiar with
JSON, which is detailed in [<cite><a class="bibref" rel="biblioentry" href="#bib-RFC4627">RFC4627</a></cite>]. To understand the API and how it is
intended to operate  in a programming environment, it is useful to have working
knowledge of the JavaScript programming language [<cite><a class="bibref" rel="biblioentry" href="#bib-ECMA-262">ECMA-262</a></cite>] and
WebIDL [<cite><a class="bibref" rel="biblioentry" href="#bib-WEBIDL">WEBIDL</a></cite>]. To understand how JSON-LD maps to RDF, it is helpful to be
familiar with the basic RDF concepts [<cite><a class="bibref" rel="biblioentry" href="#bib-RDF-CONCEPTS">RDF-CONCEPTS</a></cite>].</p>

<p>
  Examples may contain references to existing vocabularies and use <a class="tref internalDFN" title="prefix" href="#dfn-prefix">prefix</a>es to refer to Web Vocabularies. The following is a list of all vocabularies and their <a class="tref internalDFN" title="prefix" href="#dfn-prefix">prefix</a> abbreviations, as used in this document:
</p>
<ul>
  <li>The <a href="http://purl.org/dc/terms/">Dublin Core</a>
  vocabulary (abbreviation: <code>dc</code>, e.g., <code>dc:title</code>)</li>
  <li>The <a href="http://xmlns.com/foaf/0.1/">Friend of a Friend</a>
  vocabulary (abbreviation: <code>foaf</code>, e.g., <code>foaf:knows</code>)</li>
  <li>The <a href="http://www.w3.org/1999/02/22-rdf-syntax-ns#">RDF</a>
  vocabulary (abbreviation: <code>rdf</code>, e.g., <code>rdf:type</code>)</li>
  <li>The <a href="http://www.w3.org/2001/XMLSchema#">XSD</a>
  vocabulary (abbreviation: <code>xsd</code>, e.g., <code>xsd:integer</code>)</li>
</ul>

<p>
  JSON [<cite><a class="bibref" rel="biblioentry" href="#bib-RFC4627">RFC4627</a></cite>] defines several terms which are used throughout this document:
  </p><dl>
    <dt><dfn title="json_object" id="dfn-json_object">JSON Object</dfn></dt><dd>
      An object structure is represented as a pair of curly brackets surrounding zero or
      more name/value pairs (or members). A name is a <a class="tref internalDFN" title="string" href="#dfn-string">string</a>. A single colon comes after
      each name, separating the name from the value. A single comma separates a value
      from a following name. The names within an object <em class="rfc2119" title="should">should</em> be unique.
    </dd>
    <dt><dfn title="array" id="dfn-array">array</dfn></dt>
    <dd>
      An array is an ordered collection of values. An array structure is represented as square brackets surrounding zero or more values (or elements). Elements are separated by commas.  Within JSON-LD, array order is not preserved by default, unless
      specific markup is provided (see <a href="#lists">Lists</a>). This is because the basic data model of JSON-LD
      is a <a class="tref internalDFN" title="linked_data_graph" href="#dfn-linked_data_graph">linked data graph</a>, which is inherently unordered.
    </dd>
    <dt><dfn title="string" id="dfn-string">string</dfn></dt><dd>
      A string is a sequence of zero or more Unicode characters, wrapped in double quotes, using backslash escapes. A
      character is represented as a single character string.
    </dd>
    <dt><dfn title="number" id="dfn-number">number</dfn></dt>
    <dd>
      A number is is similar to that used in most programming languages, except that the octal and hexadecimal formats are not used and that leading zeros are not allowed.</dd>
    <dt><dfn title="true" id="dfn-true">true</dfn> and <dfn title="false" id="dfn-false">false</dfn></dt><dd>
      Boolean values.
    </dd>
    <dt><dfn title="null" id="dfn-null">null</dfn></dt><dd>
      The use of the <em>null</em> value is undefined within JSON-LD.
      <div class="issue">Supporting <em>null</em> in JSON-LD might have a number of advantages and should be evaluated. This is currently an <a href="https://github.com/json-ld/json-ld.org/issues/11">open issue</a>.</div>
    </dd>
  </dl>
<p></p>

</div>

<div id="syntax-tokens-and-keywords" class="section">
  <h3><span class="secno">1.2 </span>Syntax Tokens and Keywords</h3>

  <p>JSON-LD specifies a number of syntax tokens and keywords that are using
  in all algorithms described in this section:</p>

  <dl>
  <dt><code>@context</code></dt><dd>Used to set the <a class="tref internalDFN" title="local_context" href="#dfn-local_context">local context</a>.</dd>
  <dt><code>@base</code></dt><dd>Used to set the base <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a> for all object IRIs affected  by the <a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a>.</dd>
  <dt><code>@vocab</code></dt><dd>Used to set the base <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a> for all property IRIs affected by the <a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a>.</dd>
  <dt><code>@coerce</code></dt><dd>Used to specify type coercion rules.</dd>
  <dt><code>@literal</code></dt><dd>Used to specify a literal value.</dd>
  <dt><code>@iri</code></dt><dd>Used to specify an <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a> value.</dd>
  <dt><code>@language</code></dt><dd>Used to specify the language for a literal.</dd>
  <dt><code>@datatype</code></dt><dd>Used to specify the datatype for a literal.</dd>
  <dt><code>:</code></dt><dd>The separator for JSON keys and values that use the <a class="tref internalDFN" title="prefix" href="#dfn-prefix">prefix</a> mechanism.</dd>
  <dt><code>@subject</code></dt><dd>Sets the active subject.</dd>
  <dt><code>@type</code></dt><dd>Used to set the type of the active subject.</dd>
  </dl>
</div>

<div id="contributing" class="section">
<h3><span class="secno">1.3 </span>Contributing</h3>

<p>There are a number of ways that one may participate in the development of
this specification:</p>

<ul>
<li>Technical discussion typically occurs on the public mailing list:
<a href="http://lists.w3.org/Archives/Public/public-linked-json/">public-linked-json@w3.org</a>
</li>

<li><a href="http://json-ld.org/minutes/">Public teleconferences</a> are held
on Tuesdays at 1500UTC on the second and fourth week of each month.
</li>

<li>Specification bugs and issues should be reported in the
<a href="https://github.com/json-ld/json-ld.org/issues">issue tracker</a>.</li>

<li><a href="https://github.com/json-ld/json-ld.org/tree/main/spec">Source code</a> for the
specification can be found on Github.</li>

<li>The <a href="http://webchat.freenode.net/?channels=#json-ld">#json-ld</a>
IRC channel is available for real-time discussion on irc.freenode.net.</li>
</ul>

</div>

</div>

<div id="design" class="section">

<!-- OddPage -->
<h2><span class="secno">2. </span>Design</h2>

<p>The following section outlines the design goals and rationale behind the
JSON-LD markup language.
</p>

<div id="goals-and-rationale" class="section">
<h3><span class="secno">2.1 </span>Goals and Rationale</h3>

<p>
A number of design considerations were explored during the creation of this
markup language:
</p>

<dl>
 <dt>Simplicity</dt>
 <dd>Developers need only know JSON and three keywords to use the basic
 functionality in JSON-LD. No extra processors or software libraries are
 necessary to use JSON-LD in its most basic form. The language attempts to
 ensure that developers have an easy learning curve.</dd>
 <dt>Compatibility</dt>
 <dd>The JSON-LD markup must be 100% compatible with JSON. This ensures that
 all of the standard JSON libraries work seamlessly with JSON-LD documents.</dd>
 <dt>Expressiveness</dt>
 <dd>The syntax must be able to express directed graphs, which have been proven
 to be able to simply express almost every real world data model.</dd>
 <dt>Terseness</dt>
 <dd>The JSON-LD syntax must be very terse and human readable, requiring as
 little as possible effort from the developer.</dd>
 
<!-- <dt>Pragmatism</dt>
 <dd>Mixing the expression of pure Linked Data with data that is not
 linked was an approach that was driven by pragmatism. JSON-LD attempts to be
 more practical than theoretical in its approach to Linked Data.</dd> -->

 <dt>Zero Edits, most of the time</dt>
 <dd>JSON-LD provides a mechanism that allows developers to specify
 <a class="tref internalDFN" title="context" href="#dfn-context">context</a> in a way that is out-of-band. This allows organizations that have
 already deployed large JSON-based infrastructure to add meaning to their
 JSON documents in a way that is not disruptive to their day-to-day operations and is
 transparent to their current customers. At times, mapping JSON to
 a graph representation can become difficult. In these instances, rather than
 having JSON-LD support esoteric markup, we chose not to support the use case
 and support a simplified syntax instead. So, while Zero Edits is a goal,
 it is not always possible without adding great complexity to the language.
 </dd>
 <dt>One-pass Processing</dt>
 <dd>JSON-LD supports one-pass processing, which results in a very small memory 
 footprint when processing documents. For example, to convert a JSON-LD document
 into an RDF document of any kind, only one pass is required over the data.</dd>
</dl>
</div>

<div id="linked-data" class="section">
<h3><span class="secno">2.2 </span>Linked Data</h3>
<p>
The following definition for <a class="tref internalDFN" title="linked_data" href="#dfn-linked_data">Linked Data</a> is the one that will
be used for this specification.
</p>
<ol>
  <li><dfn title="linked_data" id="dfn-linked_data">Linked Data</dfn> is a set of documents, each containing a representation of a linked data graph.</li>
  <li>A <dfn title="linked_data_graph" id="dfn-linked_data_graph">linked data graph</dfn> is an unordered labeled directed graph, where nodes are <a class="tref internalDFN" title="subject" href="#dfn-subject">subject</a>s or <a class="tref internalDFN" title="object" href="#dfn-object">object</a>s, and edges are properties.</li>
  <li>A <dfn title="subject" id="dfn-subject">subject</dfn> is any node in a <a class="tref internalDFN" title="linked_data_graph" href="#dfn-linked_data_graph">linked data graph</a> with at least one outgoing edge.</li>
  <li>A <a class="tref internalDFN" title="subject" href="#dfn-subject">subject</a> <em class="rfc2119" title="should">should</em> be labeled with an <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a> (an Internationalized Resource Identifier as described in [<cite><a class="bibref" rel="biblioentry" href="#bib-RFC3987">RFC3987</a></cite>]).</li>
  <li>An <dfn title="object" id="dfn-object">object</dfn> is a node in a <a class="tref internalDFN" title="linked_data_graph" href="#dfn-linked_data_graph">linked data graph</a> with at least one incoming edge.</li>
  <li>An <a class="tref internalDFN" title="object" href="#dfn-object">object</a> <em class="rfc2119" title="may">may</em> be labeled with an <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>.</li>
  <li>An object <em class="rfc2119" title="may">may</em> be a <a class="tref internalDFN" title="subject" href="#dfn-subject">subject</a> and <a class="tref internalDFN" title="object" href="#dfn-object">object</a> at the same time.</li>
  <li>A <dfn title="property" id="dfn-property">property</dfn> is an edge of the <a class="tref internalDFN" title="linked_data_graph" href="#dfn-linked_data_graph">linked data graph</a>.</li>
  <li>A <a class="tref internalDFN" title="property" href="#dfn-property">property</a> <em class="rfc2119" title="should">should</em> be labeled with an <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>.</li>
  <li>An <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a> that is a label in a <a class="tref internalDFN" title="linked_data_graph" href="#dfn-linked_data_graph">linked data graph</a> <em class="rfc2119" title="should">should</em> be dereferencable to a <a class="tref internalDFN" title="linked_data" href="#dfn-linked_data">Linked Data</a> document describing the labeled <a class="tref internalDFN" title="subject" href="#dfn-subject">subject</a>, <a class="tref internalDFN" title="object" href="#dfn-object">object</a> or <a class="tref internalDFN" title="property" href="#dfn-property">property</a>.</li>
  <li>A <dfn title="literal" id="dfn-literal">literal</dfn> is an <a class="tref internalDFN" title="object" href="#dfn-object">object</a> with a label that is not an <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a></li>
</ol>

<p>
Note that the definition for <a class="tref internalDFN" title="linked_data" href="#dfn-linked_data">Linked Data</a> above is silent on the
topic of unlabeled nodes. Unlabeled nodes are not considered
<a class="tref internalDFN" title="linked_data" href="#dfn-linked_data">Linked Data</a>. However, this specification allows for the expression
of unlabled nodes, as most graph-based data sets on the Web contain a number
of associated nodes that are not named and thus are not directly
de-referenceable.
</p>
</div>

<div id="linking-data" class="section">
<h3><span class="secno">2.3 </span>Linking Data</h3>

<p>
An Internationalized Resource Identifier
(<dfn title="iri" id="dfn-iri"><abbr title="Internationalized Resource Identifier">IRI</abbr></dfn>),
as described in [<cite><a class="bibref" rel="biblioentry" href="#bib-RFC3987">RFC3987</a></cite>], is a mechanism for representing unique
identifiers on the web. In <a class="tref internalDFN" title="linked_data" href="#dfn-linked_data">Linked Data</a>, an IRI is commonly
used for expressing a <a class="tref internalDFN" title="subject" href="#dfn-subject">subject</a>, a <a class="tref internalDFN" title="property" href="#dfn-property">property</a> or an
<a class="tref internalDFN" title="object" href="#dfn-object">object</a>.
</p>

<p>JSON-LD defines a mechanism to map JSON terms, i.e., keys and values, to IRIs. This does not mean
that JSON-LD requires every key or value to be an IRI, but rather ensures that
keys and values can be mapped to IRIs if the developer desires to transform
their data into <a class="tref internalDFN" title="linked_data" href="#dfn-linked_data">Linked Data</a>. There are a few techniques that can ensure
that developers will generate good Linked Data for the Web. JSON-LD
formalizes those techniques.
</p>

<p>We will be using the following JSON markup as the example for the
rest of this section:
</p>

<pre class="example">{
  &quot;name&quot;: &quot;Manu Sporny&quot;,
  &quot;homepage&quot;: &quot;http://manu.sporny.org/&quot;,
  &quot;avatar&quot;: &quot;http://twitter.com/account/profile_image/manusporny&quot;
}</pre>
</div>

<div id="the-context" class="section">
<h3><span class="secno">2.4 </span>The Context</h3>

<p>In JSON-LD, a <dfn title="context" id="dfn-context">context</dfn> is used to map <a class="tref internalDFN" title="term" href="#dfn-term">term</a>s, i.e., keys and values
  in an JSON document, to
  <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>s. A <dfn title="term" id="dfn-term">term</dfn> is a short word that <em class="rfc2119" title="may">may</em> be expanded
to an <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>. The Web uses IRIs for unambiguous identification. The
idea is that these <a class="tref internalDFN" title="term" href="#dfn-term">term</a>s mean something that may be of use to
other developers and that it is useful to give them an unambiguous identifier.
That is, it is useful for <a class="tref internalDFN" title="term" href="#dfn-term">term</a>s to expand to IRIs so that
developers don't accidentally step on each other's Web Vocabulary terms.
For example, the term <code>name</code> may map directly to the IRI
<code>http://xmlns.com/foaf/0.1/name</code>. This allows JSON-LD documents to
be constructed using the common JSON practice of simple name/value pairs while
ensuring that the data is useful outside of the page, API or database in which it
resides.
</p>

<p>These Linked Data <a class="tref internalDFN" title="term" href="#dfn-term">term</a>s are typically collected in a context document that would look something like this:</p>

<pre class="example">{
  &quot;@context&quot;: {
    &quot;name&quot;: &quot;http://xmlns.com/foaf/0.1/name&quot;,
    &quot;homepage&quot;: &quot;http://xmlns.com/foaf/0.1/homepage&quot;,
    &quot;avatar&quot;: &quot;http://xmlns.com/foaf/0.1/avatar&quot;
  }
}</pre>

<p>This context document can then be used in an JSON-LD document by adding a 
single line. The JSON markup as shown in the previous section could be changed 
as follows to link to the context document:</p>

<pre class="example">{
  <span class="diff">&quot;@context&quot;: &quot;http://example.org/json-ld-contexts/person&quot;,</span>
  &quot;name&quot;: &quot;Manu Sporny&quot;,
  &quot;homepage&quot;: &quot;http://manu.sporny.org/&quot;,
  &quot;avatar&quot;: &quot;http://twitter.com/account/profile_image/manusporny&quot;
}</pre>

<p>The additions above transform the previous JSON document into a JSON document
with added semantics because the <code>@context</code> specifies how the
<strong>name</strong>, <strong>homepage</strong>, and <strong>avatar</strong>
terms map to IRIs.
Mapping those keys to IRIs gives the data global context. If two
developers use the same IRI to describe a property, they are more than likely
expressing the same concept. This allows both developers to re-use each others
data without having to agree to how their data will inter-operate on a
site-by-site basis. Contexts may also contain datatype information
for certain <a class="tref internalDFN" title="term" href="#dfn-term">term</a>s as well as other processing instructions for
the JSON-LD processor.</p>

<p>Contexts may be specified in-line. This ensures that JSON-LD documents
can be processed when a JSON-LD processor does not have access to the Web.</p>

<pre class="example">{
  <span class="diff">&quot;@context&quot;: {
    &quot;name&quot;: &quot;http://xmlns.com/foaf/0.1/name&quot;,
    &quot;homepage&quot;: &quot;http://xmlns.com/foaf/0.1/homepage&quot;,
    &quot;avatar&quot;: &quot;http://xmlns.com/foaf/0.1/avatar&quot;
  },</span>
  &quot;name&quot;: &quot;Manu Sporny&quot;,
  &quot;homepage&quot;: &quot;http://manu.sporny.org/&quot;,
  &quot;avatar&quot;: &quot;http://twitter.com/account/profile_image/manusporny&quot;
}</pre>

<p>Contexts may be used at any time a <a class="tref internalDFN" title="json_object" href="#dfn-json_object">JSON object</a> is defined, and a <a class="tref internalDFN" title="json_object" href="#dfn-json_object">JSON object</a>
  may specify multiple contexts, to be processed in order, for example to include standard prefix
  definitions along with a local language definition used to set the language of <a class="tref internalDFN" title="plain_literal" href="#dfn-plain_literal">plain literal</a>s:</p>

<p>
  The set of contexts defined within a specific <a class="tref internalDFN" title="json_object" href="#dfn-json_object">JSON Object</a> is termed a <dfn title="local_context" id="dfn-local_context">local context</dfn>.
  The <dfn title="active_context" id="dfn-active_context">active context</dfn> refers to the accumulation of <a class="tref internalDFN" title="local_context" href="#dfn-local_context">local context</a>s that are in scope
  at a specific point within the document.</p>

<pre class="example">{
  <span class="diff">&quot;@context&quot;: [
    &quot;http://example.org/json-ld-contexts/person&quot;,
    {
      &quot;@language&quot;: &quot;en&quot;
    }
  ],</span>
  &quot;name&quot;: &quot;Manu Sporny&quot;,
  &quot;homepage&quot;: &quot;http://manu.sporny.org/&quot;,
  &quot;avatar&quot;: &quot;http://twitter.com/account/profile_image/manusporny&quot;
}</pre>

<p>JSON-LD strives to ensure that developers don't have to change the JSON
  that is going into and being returned from their Web APIs. This means
  that developers can also specify a <a class="tref internalDFN" title="context" href="#dfn-context">context</a> for JSON data in an out-of-band
  fashion. This is described later in this document. </p>

<p>
  JSON-LD uses a special type of machine-readable document called a
  <dfn title="web_vocabulary" id="dfn-web_vocabulary">Web Vocabulary</dfn> to define <a class="tref internalDFN" title="term" href="#dfn-term">term</a>s that are then used
  to describe concepts and &quot;things&quot; in the world.
  Typically, these Web Vocabulary documents have <a class="tref internalDFN" title="prefix" href="#dfn-prefix">prefix</a>es associated
  with them and contain a number of <a class="tref internalDFN" title="term" href="#dfn-term">term</a> declarations.
  <a class="tref internalDFN" title="prefix" href="#dfn-prefix">Prefix</a>es are helpful when a developer
  wants to mix multiple vocabularies together in a <a class="tref internalDFN" title="context" href="#dfn-context">context</a>, but does not want
  to go to the trouble of defining every single term in every single vocabulary.
  Some Web Vocabularies may have dozens of terms defined. If a developer wants to use
  3-4 different vocabularies, the number of terms that
  would have to be declared in a single <a class="tref internalDFN" title="context" href="#dfn-context">context</a> could become quite large. To
  reduce the number of different terms that must be defined, JSON-LD also allows
  prefixes to be used to compact IRIs.
</p><p>

</p><p>For example, the <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a> <code>http://xmlns.com/foaf/0.1/</code>
specifies a <a class="tref internalDFN" title="web_vocabulary" href="#dfn-web_vocabulary">Web Vocabulary</a> which may be represented using the
<code>foaf</code> <a class="tref internalDFN" title="prefix" href="#dfn-prefix">prefix</a>. The <code>foaf</code> Web Vocabulary
contains a term called <strong>name</strong>. If you join the
<code>foaf</code> <a class="tref internalDFN" title="prefix" href="#dfn-prefix">prefix</a> with the <strong>name</strong> suffix,
you can build a compact IRI that will expand out into an absolute IRI for the
<code>http://xmlns.com/foaf/0.1/name</code> vocabulary term.
That is, the compact IRI, or short-form, is <code>foaf:name</code> and the
expanded-form is <code>http://xmlns.com/foaf/0.1/name</code>. This vocabulary
term is used to specify a person's name.
</p>

<p>Developers, and machines, are able to use this <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a> (plugging it
directly into a web browser, for instance) to go to the term and get a
definition of what the term means. Much like we can use <a href="http://wordnet.princeton.edu/">WordNet</a> today to
see the definition
of words in the English language. Developers and machines need the same sort of
definition of terms. IRIs provide a way to ensure that these terms
are unambiguous.
</p>

<p>The <a class="tref internalDFN" title="context" href="#dfn-context">context</a> provides a collection of vocabulary <a class="tref internalDFN" title="term" href="#dfn-term">term</a>s and
<a class="tref internalDFN" title="prefix" href="#dfn-prefix">prefix</a>es that can be used to expand JSON keys and values into
<a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>s.</p>

<p class="note">To ensure the best possible performance, it is a best practice to
put the <a class="tref internalDFN" title="context" href="#dfn-context">context</a> definition at the top of the JSON-LD document. If it isn't listed
first, processors have to save each key-value pair until the <a class="tref internalDFN" title="context" href="#dfn-context">context</a> is processed.
This creates a memory and complexity burden for one-pass processors.</p>
<div id="external-contexts" class="section">
  <h4><span class="secno">2.4.1 </span>External Contexts</h4>

  <p>Authors may choose to declare JSON-LD <a class="tref internalDFN" title="context" href="#dfn-context">context</a>s in external 
documents to promote re-use of contexts as well as reduce the size of JSON-LD 
documents.
In order to use an external context, an author <em class="rfc2119" title="may">may</em> specify an <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a> to a valid
JSON-LD document. The referenced document <em class="rfc2119" title="must">must</em> have a top-level <a class="tref internalDFN" title="json_object" href="#dfn-json_object">JSON Object</a>.
The value of any <code>@context</code> key within that object is substituted for
the IRI within the referencing document to have the same effect as if the value were
specified inline within the referencing document.</p>
  <p>The following example demonstrates the use of an external context:</p>

<pre class="example">{
  <span class="diff">&quot;@context&quot;: &quot;http://example.org/json-ld-contexts/person&quot;</span>,
  &quot;name&quot;: &quot;Manu Sporny&quot;,
  &quot;homepage&quot;: &quot;http://manu.sporny.org/&quot;,
  &quot;avatar&quot;: &quot;http://twitter.com/account/profile_image/manusporny&quot;
}</pre>

<p>Authors may also import multiple contexts or a combination of external and local contexts by specifying a list of 
contexts:</p>

<pre class="example">{
  <span class="diff">&quot;@context&quot;: [&quot;http://example.org/json-ld-contexts/person&quot;, &quot;http://example.org/json-ld-contexts/event&quot;]</span>
  &quot;name&quot;: &quot;Manu Sporny&quot;,
  &quot;homepage&quot;: &quot;http://manu.sporny.org/&quot;,
  &quot;avatar&quot;: &quot;http://twitter.com/account/profile_image/manusporny&quot;
  <span class="diff">&quot;celebrates&quot;:
  {
     &quot;@type&quot;: &quot;Event&quot;,
     &quot;description&quot;: &quot;International Talk Like a Pirate Day&quot;,
     &quot;date&quot;: &quot;R/2011-09-19&quot;
  }</span>
}</pre>

<p>Each context in a list will be evaluated in-order. Duplicate mappings within the <a class="tref internalDFN" title="context" href="#dfn-context">context</a>s <em class="rfc2119" title="must">must</em> be
overwritten on a last-defined-overrides basis. The context list <em class="rfc2119" title="must">must</em> contain
either de-referenceable <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>s or <a class="tref internalDFN" title="json_object" href="#dfn-json_object">JSON Object</a>s that conform to the
<a class="tref internalDFN" title="context" href="#dfn-context">context</a> syntax as described in this document.</p>

<p>External JSON-LD context documents <em class="rfc2119" title="may">may</em> contain extra information located
outside of the <code>@context</code> key, such as
documentation about the <a class="tref internalDFN" title="prefix" href="#dfn-prefix">prefix</a>es declared in the document. It is
also <em class="rfc2119" title="recommended">recommended</em> that a human-readable document encoded in HTML+RDFa 
[<cite><a class="bibref" rel="biblioentry" href="#bib-HTML-RDFA">HTML-RDFA</a></cite>] or other Linked Data compatible format is served as well to
explain the correct usage of the JSON-LD context document.
</p>

</div>

</div>

<div id="from-json-to-json-ld" class="section">
<h3><span class="secno">2.5 </span>From JSON to JSON-LD</h3>

<p>If a set of terms such as, <strong>name</strong>, <strong>homepage</strong>,
and <strong>avatar</strong>,
are defined in a <a class="tref internalDFN" title="context" href="#dfn-context">context</a>, and that context is used to resolve the
names in JSON objects, machines are able to automatically expand the terms to
something meaningful and unambiguous, like this:</p>

<pre class="example">{
  &quot;<span class="diff">http://xmlns.com/foaf/0.1/name</span>&quot;: &quot;Manu Sporny&quot;,
  &quot;<span class="diff">http://xmlns.com/foaf/0.1/homepage</span>&quot;: &quot;http://manu.sporny.org&quot;
  &quot;<span class="diff">http://rdfs.org/sioc/ns#avatar</span>&quot;: &quot;http://twitter.com/account/profile_image/manusporny&quot;
}</pre>

<p>Doing this allows JSON to be unambiguously machine-readable without
requiring developers to drastically change their workflow.</p>
<p class="note">Please note that this JSON-LD document doesn't define the
subject and will thus result in an unlabeled or blank node.</p>

</div>

</div>



<div id="basic-concepts" class="section">

<!-- OddPage -->
<h2><span class="secno">3. </span>Basic Concepts</h2>

<p>JSON-LD is designed to ensure that <a class="tref internalDFN" title="linked_data" href="#dfn-linked_data">Linked Data</a> concepts can be marked
up in a way that is simple to understand and author by Web developers. In many
cases, regular JSON markup can become Linked Data with the simple addition
of a <a class="tref internalDFN" title="context" href="#dfn-context">context</a>. As more JSON-LD features are used, more semantics are added
to the JSON markup.</p>

<div id="iris" class="section">
<h3><span class="secno">3.1 </span>IRIs</h3>

<p>Expressing <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>s are fundamental to <a class="tref internalDFN" title="linked_data" href="#dfn-linked_data">Linked Data</a> as that is how most
<a class="tref internalDFN" title="subject" href="#dfn-subject">subject</a>s and many <a class="tref internalDFN" title="object" href="#dfn-object">object</a> are named. <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>s can be
expressed in a variety of different ways in JSON-LD.</p>

<ol>
  <li>In general, <a class="tref internalDFN" title="term" href="#dfn-term">term</a>s in the key position in
    a <a class="tref internalDFN" title="json_object" href="#dfn-json_object">JSON object</a> that have a mapping to an <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a> or another key in the <a class="tref internalDFN" title="context" href="#dfn-context">context</a> are
    expanded to an IRI by JSON-LD processors. There are special rules for
    processing keys in <code>@context</code> and when dealing with keys that
    start with the <code>@subject</code> character.</li>
  <li>An <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a> is generated for the value specified using <code>@subject</code>,
    if it is a <a class="tref internalDFN" title="string" href="#dfn-string">string</a>.</li>
  <li>An <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a> is generated for the value specified using <code>@type</code>.</li>
  <li>An <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a> is generated for the value specified using the <code>@iri</code>
    keyword.</li>
  <li>An <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a> is generated when there are <code>@coerce</code> rules in
    effect for a key named <code>@iri</code>.</li>
</ol>

<p>IRIs can be expressed directly in the key position like so:
</p>

<pre class="example">{
...
  &quot;<span class="diff">http://xmlns.com/foaf/0.1/name</span>&quot;: &quot;Manu Sporny&quot;,
...
}</pre>

<p>In the example above, the key
<code>http://xmlns.com/foaf/0.1/name</code> is interpreted as an <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>, as
opposed to being interpreted as a string.</p>

<p>Term expansion occurs for IRIs if a term is defined within the
<a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a>:</p>

<pre class="example">{
  &quot;<span class="diff">@context</span>&quot;: {&quot;<span class="diff">name</span>&quot;: &quot;<span class="diff">http://xmlns.com/foaf/0.1/name</span>&quot;},
...
  &quot;<span class="diff">name</span>&quot;: &quot;Manu Sporny&quot;,
...
}</pre>

<p><a class="tref internalDFN" title="prefix" href="#dfn-prefix">Prefix</a>es are expanded when used in keys:</p>

<pre class="example">{
  &quot;<span class="diff">@context</span>&quot;: {&quot;<span class="diff">foaf</span>&quot;: &quot;<span class="diff">http://xmlns.com/foaf/0.1/</span>&quot;},
...
  &quot;<span class="diff">foaf:name</span>&quot;: &quot;Manu Sporny&quot;,
...
}</pre>

<p><code>foaf:name</code> above will automatically expand out to the IRI
<code>http://xmlns.com/foaf/0.1/name</code>.</p>

<p>An <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a> is generated when a value is associated with a key using
the <code>@iri</code> keyword:</p>

<pre class="example">{
...
  &quot;homepage&quot;: { &quot;<span class="diff">@iri</span>&quot;: &quot;http://manu.sporny.org&quot; }
...
}</pre>

<p>If type coercion rules are specified in the <code>@context</code> for
a particular vocabulary term, an IRI is generated:</p>

<pre class="example">{<span class="diff">
  &quot;@context&quot;:
  {
    ...
    &quot;@coerce&quot;:
    {
      &quot;@iri&quot;: &quot;homepage&quot;
    }
  }</span>
...
  &quot;homepage&quot;: &quot;http://manu.sporny.org/&quot;,
...
}</pre>

<p>Even though the value <code>http://manu.sporny.org/</code> is a <a class="tref internalDFN" title="string" href="#dfn-string">string</a>,
the type coercion rules will transform the value into an IRI when processed
by a JSON-LD Processor</p>

<p>IRIs may be represented as an absolute IRI, a <a class="tref internalDFN" title="term" href="#dfn-term">term</a>, a <a class="tref internalDFN" title="prefix" href="#dfn-prefix">prefix</a>:<a class="tref internalDFN" title="term" href="#dfn-term">term</a> construct, or as a value relative to <code>@base</code> or <code>@vocab</code>.</p>

</div>

<div id="identifying-the-subject" class="section">
<h3><span class="secno">3.2 </span>Identifying the Subject</h3>

<p>
  To be able to externally reference nodes, it is important that each node has an unambiguous identifier.
  <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>s are a fundamental concept of <a class="tref internalDFN" title="linked_data" href="#dfn-linked_data">Linked Data</a>, and nodes should have a de-referencable
  identifier used to name and locate them. For nodes to be truely linked, de-referencing the identifier
  should result in a representation of that node. Associating an IRI with a node tells an application
  that the returned document contains a description of the node requested.
</p>
<p>
  JSON-LD documents may also contain descriptions of other nodes, so it is necessary to be able to
  uniquely identify each node which may be externally referenced.
</p>
<p>A <a class="tref internalDFN" title="subject" href="#dfn-subject">subject</a>
   of an object in JSON is declared using the <code>@subject</code> key. The subject is the
first piece of information needed by the JSON-LD processor in order to
create the (subject, property, object) tuple, also known as a triple.</p>

<pre class="example">{
...
  &quot;<span class="diff">@subject</span>&quot;: &quot;<span class="diff">http://example.org/people#joebob</span>&quot;,
...
}</pre>

<p>The example above would set the subject to the IRI
<code>http://example.org/people#joebob</code>.
</p>

<p class="note">To ensure the best possible performance, it is a best practice to
put the <code>@subject</code> key before other key-value pairs in an object. If
it isn't listed first, processors have to save each key-value pair until
<code>@subject</code> is processed before they can create valid triples. This
creates a memory and complexity burden for one-pass processors.</p>

</div>

<div id="specifying-the-type" class="section">
<h3><span class="secno">3.3 </span>Specifying the Type</h3>

<p>The type of a particular subject can be specified using the
<code>@type</code> key. Specifying the type in this way will generate a
triple of the form (subject, type, type-iri).</p>

<p>To be <a class="tref internalDFN" title="linked_data" href="#dfn-linked_data">Linked Data</a>, types <em class="rfc2119" title="must">must</em> be uniquely identified by an
  <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>.</p>

<pre class="example">{
...
  &quot;@subject&quot;: &quot;http://example.org/people#joebob&quot;,
  &quot;<span class="diff">@type</span>&quot;: &quot;<span class="diff">http://xmlns.com/foaf/0.1/Person</span>&quot;,
...
}</pre>

<p>The example above would generate the following triple if the JSON-LD
document is mapped to RDF (in N-Triples notation):</p>

<pre class="example">&lt;http://example.org/people#joebob&gt;
   &lt;http://www.w3.org/1999/02/22-rdf-syntax-ns#type&gt;
      &lt;http://xmlns.com/foaf/0.1/Person&gt; .</pre>

</div>

<div id="strings" class="section">
<h3><span class="secno">3.4 </span>Strings</h3>

<p>Regular text strings, also referred to as <dfn title="plain_literal" id="dfn-plain_literal">plain literal</dfn>s, are
easily expressed using regular JSON <a class="tref internalDFN" title="string" href="#dfn-string">string</a>s.</p>

<pre class="example">{
...
  &quot;name&quot;: &quot;<span class="diff">Mark Birbeck</span>&quot;,
...
}</pre>

</div>

<div id="string-internationalization" class="section">
<h3><span class="secno">3.5 </span>String Internationalization</h3>

<p>JSON-LD makes an assumption that strings with associated language encoding
information are not very common when used in JavaScript and Web Services.
Thus, it takes a little more effort to express strings with associated
language information.</p>

<pre class="example">{
...
  &quot;name&quot;: <span class="diff">
  {
    &quot;@literal&quot;: &quot;花澄&quot;,
    &quot;@language&quot;: &quot;ja&quot;
  }</span>
...
}</pre>

<p>The example above would generate a <a class="tref internalDFN" title="plain_literal" href="#dfn-plain_literal">plain literal</a> for
<em>花澄</em> and associate the <code>ja</code> language code with the triple
that is generated. Languages <em class="rfc2119" title="must">must</em> be expressed in [<cite><a class="bibref" rel="biblioentry" href="#bib-BCP47">BCP47</a></cite>] format.</p>

<p>It is also possible to set a language to use within a <code>@context</code>, to allow specify a language
to apply to all <a class="tref internalDFN" title="plain_literal" href="#dfn-plain_literal">plain literal</a>s within the scope of the <a class="tref internalDFN" title="context" href="#dfn-context">context</a></p>

<pre class="example">{
  <span class="diff">&quot;@context:&quot; {
    &quot;@language&quot;: &quot;ja&quot;
  },</span>
...
  &quot;name&quot;: <span class="diff">&quot;花澄&quot;</span>
...
}</pre>
</div>

<div id="typed-literals" class="section">
<h3><span class="secno">3.6 </span>Typed Literals</h3>

<p>
  A value with an associated datatype, also known as a
  <dfn title="typed_literal" id="dfn-typed_literal">typed literal</dfn>, is indicated by associating a literal with
  an <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a> which indicates the literal's datatype. Typed literals may be
  expressed in JSON-LD in three ways:
</p>

<ol>
  <li>By utilizing the <code>@coerce</code> keyword.</li>
  <li>By utilizing the expanded form for specifying objects.</li>
  <li>By using a native JSON datatype.</li>
</ol>

<p>The first example uses the <code>@coerce</code> keyword to express a
typed literal:</p>

<pre class="example">{<span class="diff">
  &quot;@context&quot;:
  {
    &quot;modified&quot;:  &quot;http://purl.org/dc/terms/modified&quot;,
    &quot;dateTime&quot;: &quot;http://www.w3.org/2001/XMLSchema#dateTime&quot;
    &quot;@coerce&quot;:
    {
      &quot;dateTime&quot;: &quot;modified&quot;
    }
  }</span>
...
  &quot;modified&quot;: &quot;2010-05-29T14:17:39+02:00&quot;,
...
}</pre>

<p>The second example uses the expanded form for specifying objects:</p>

<pre class="example">{
...
  &quot;modified&quot;: <span class="diff">
  {
    &quot;@literal&quot;: &quot;2010-05-29T14:17:39+02:00&quot;,
    &quot;@datatype&quot;: &quot;dateTime&quot;
  }</span>
...
}</pre>

<p>Both examples above would generate an object with the literal value of
<code>2010-05-29T14:17:39+02:00</code> and the datatype of
<code>http://www.w3.org/2001/XMLSchema#dateTime</code>.</p>

<p>The third example uses a built-in native JSON type, a
  <a class="tref internalDFN" title="number" href="#dfn-number">number</a>, to express a datatype:</p>

<pre class="example">{
...
  &quot;@subject&quot;: &quot;http://example.org/people#joebob&quot;,
  &quot;age&quot;: <span class="diff">31</span>
...
}</pre>

<p>The example above would generate the following triple:</p>

<pre class="example">&lt;http://example.org/people#joebob&gt;
   &lt;http://xmlns.com/foaf/0.1/age&gt;
      &quot;31&quot;^^&lt;http://www.w3.org/2001/XMLSchema#integer&gt; .</pre>

</div>

<div id="multiple-objects-for-a-single-property" class="section">
<h3><span class="secno">3.7 </span>Multiple Objects for a Single Property</h3>

<p>A JSON-LD author can express multiple triples in a compact way by using
<a class="tref internalDFN" title="array" href="#dfn-array">array</a>s. If a subject has multiple values for the same property, the author
<em class="rfc2119" title="may">may</em> express each property as an <a class="tref internalDFN" title="array" href="#dfn-array">array</a>.</p>

<p class="note">In JSON-LD, multiple objects on a property are not ordered. This is because typically graphs
are not inherently ordered data structures. To see more on creating ordered collections
in JSON-LD, see <a href="#lists">Lists</a>.
</p>

<pre class="example">{
...
  &quot;@subject&quot;: &quot;http://example.org/people#joebob&quot;,
  &quot;nick&quot;: <span class="diff">[&quot;joe&quot;, &quot;bob&quot;, &quot;jaybee&quot;]</span>,
...
}</pre>

<p>The markup shown above would generate the following triples:</p>

<pre class="example">&lt;http://example.org/people#joebob&gt;
   &lt;http://xmlns.com/foaf/0.1/nick&gt;
      &quot;joe&quot; .
&lt;http://example.org/people#joebob&gt;
   &lt;http://xmlns.com/foaf/0.1/nick&gt;
      &quot;bob&quot; .
&lt;http://example.org/people#joebob&gt;
   &lt;http://xmlns.com/foaf/0.1/nick&gt;
      &quot;jaybee&quot; .</pre>

</div>

<div id="multiple-typed-literals-for-a-single-property" class="section">
<h3><span class="secno">3.8 </span>Multiple Typed Literals for a Single Property</h3>

<p>Multiple <a class="tref internalDFN" title="typed_literal" href="#dfn-typed_literal">typed literal</a>s may also be expressed using the expanded
form for objects:</p>

<pre class="example">{
...
  &quot;@subject&quot;: &quot;http://example.org/articles/8&quot;,
  &quot;modified&quot;: <span class="diff">
  [
    {
      &quot;@literal&quot;: &quot;2010-05-29T14:17:39+02:00&quot;,
      &quot;@datatype&quot;: &quot;dateTime&quot;
    },
    {
      &quot;@literal&quot;: &quot;2010-05-30T09:21:28-04:00&quot;,
      &quot;@datatype&quot;: &quot;dateTime&quot;
    }
  ]</span>
...
}</pre>

<p>The markup shown above would generate the following triples:</p>

<pre class="example">&lt;http://example.org/articles/8&gt;
   &lt;http://purl.org/dc/terms/modified&gt;
      &quot;2010-05-29T14:17:39+02:00&quot;^^http://www.w3.org/2001/XMLSchema#dateTime .
&lt;http://example.org/articles/8&gt;
   &lt;http://purl.org/dc/terms/modified&gt;
      &quot;2010-05-30T09:21:28-04:00&quot;^^http://www.w3.org/2001/XMLSchema#dateTime .</pre>

</div>

<div id="lists" class="section">
  <h3><span class="secno">3.9 </span>Lists</h3>
  <p>
    Because graphs do not describe ordering for links between nodes,  in contrast to plain JSON, multi-valued properties
    in JSON-LD do not provide an ordering of the listed objects. For example, consider the following
    simple document:
  </p>
  <pre class="example">{
...
  &quot;@subject&quot;: &quot;http://example.org/people#joebob&quot;,
  &quot;nick&quot;: <span class="diff">[&quot;joe&quot;, &quot;bob&quot;, &quot;jaybee&quot;]</span>,
...
}</pre>
  <p>
    This results in three triples being generated, each relating the subject to an individual
    object, with no inherent order.</p>
  <p>To preserve the order of the objects, RDF-based languages, such as [<cite><a class="bibref" rel="biblioentry" href="#bib-TURTLE">TURTLE</a></cite>]
    use the concept of an <code>rdf:List</code> (as described in [<cite><a class="bibref" rel="biblioentry" href="#bib-RDF-SCHEMA">RDF-SCHEMA</a></cite>]). This uses a sequence
    of unlabeled nodes with properties describing a value, a null-terminated next property. Without
    specific syntactical support, this could be represented in JSON-LD as follows:
  </p>
  <pre class="example">{
...
  &quot;@subject&quot;: &quot;http://example.org/people#joebob&quot;,
  &quot;nick&quot;: <span class="diff">{</span>,
    <span class="diff">&quot;@first&quot;: &quot;joe&quot;</span>,
    <span class="diff">&quot;@rest&quot;: {</span>
      <span class="diff">&quot;@first&quot;: &quot;bob&quot;</span>,
      <span class="diff">&quot;@rest&quot;: {</span>
        <span class="diff">&quot;@first&quot;: &quot;jaybee&quot;</span>,
        <span class="diff">&quot;@rest&quot;: &quot;@nil&quot;</span>
        <span class="diff">}</span>
      <span class="diff">}</span>
    <span class="diff">}</span>
  <span class="diff">}</span>,
...
}</pre>
  <p>
    As this notation is rather unwieldy and the notion of ordered collections is rather important
    in data modeling, it is useful to have specific language support. In JSON-LD, a list may
    be represented using the <code>@list</code> keyword as follows:
  </p>
  <pre class="example">{
...
  &quot;@subject&quot;: &quot;http://example.org/people#joebob&quot;,
  &quot;foaf:nick&quot;: <span class="diff">{&quot;@list&quot;: [&quot;joe&quot;, &quot;bob&quot;, &quot;jaybee&quot;]}</span>,
...
}</pre>
  <p>
    This describes the use of this <a class="tref internalDFN" title="array" href="#dfn-array">array</a> as being ordered, and order is maintained through normalization
    and RDF conversion as described in [<cite><a class="bibref" rel="biblioentry" href="#bib-JSON-LD-API">JSON-LD-API</a></cite>]. If every use of a given multi-valued property is a list, this
    may be abbreviated by adding an <code>@coerce</code> term:
  </p>
  <pre class="example">{
  <span class="diff">&quot;@context&quot;: {</span>
    ...
    <span class="diff">&quot;@coerce&quot;: {</span>
      <span class="diff">&quot;@list&quot;: [&quot;foaf:nick&quot;]</span>
    <span class="diff">}</span>
  <span class="diff">}</span>,
...
  &quot;@subject&quot;: &quot;http://example.org/people#joebob&quot;,
  &quot;foaf:nick&quot;: <span class="diff">[&quot;joe&quot;, &quot;bob&quot;, &quot;jaybee&quot;]</span>,
...
}</pre>
  <p>
    The @list keyword can be used within the <code>@coerce</code> section of a <code>@context</code> to
    cause value arrays to be coerced into an ordered list.
  </p>
</div>

</div>

<div id="advanced-concepts" class="section">

<!-- OddPage -->
<h2><span class="secno">4. </span>Advanced Concepts</h2>

<p>JSON-LD has a number of features that provide functionality above and beyond
the core functionality described above. The following sections outline the
features that are specific to JSON-LD.
</p>


<div id="base-uri" class="section">
<h3><span class="secno">4.1 </span>Base URI</h3>
<p>JSON-LD allows <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>s to be specified in a relative form. For <a class="tref internalDFN" title="subject" href="#dfn-subject">subject</a> and <a class="tref internalDFN" title="object" href="#dfn-object">object</a>
  IRIs, relative IRIs are resolved against the document base using
  <cite><a href="http://www.ietf.org/rfc/rfc2396.txt">section 5.1 Establishing a
  Base URI</a></cite> of [<cite><a class="bibref" rel="biblioentry" href="#bib-RFC3986">RFC3986</a></cite>]. This value may be explicitly
  set with a <a class="tref internalDFN" title="context" href="#dfn-context">context</a> using the <code>@base</code> keyword.</p>

<p>For example, if a JSON-LD document was retrieved from <code>http://manu.sporny.org/</code>,
  relative IRIs would resolve against that URI:</p>

<pre class="example">{
  <span class="diff">&quot;@subject&quot;: &quot;about/&quot;</span>,
  &quot;http://xmlns.com/foaf/0.1/name&quot;: &quot;Manu Sporny&quot;,
  &quot;http://xmlns.com/foaf/0.1/homepage: &quot;&quot;
}</pre>

<p>This document uses an empty <code>@subject</code>, which resolves to the document base. However, if
  the document is moved to a different location, the subject IRI would change. To prevent this, a <a class="tref internalDFN" title="context" href="#dfn-context">context</a>
  may have a <code>@base</code> mapping, to set an absolute base for the document in spite of where
  it actually is retrieved from. It <em class="rfc2119" title="must">must</em> have a value of a simple
  <a class="tref internalDFN" title="string" href="#dfn-string">string</a> with the lexical form of an absolute <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>.</p>

<pre class="example">{
  <span class="diff">&quot;@context&quot;: { &quot;@base&quot;: &quot;http://manu.sporny.org/&quot;}</span>,
  &quot;@subject&quot;: &quot;about/&quot;,
  &quot;http://xmlns.com/foaf/0.1/name&quot;: &quot;Manu Sporny&quot;,
  &quot;http://xmlns.com/foaf/0.1/homepage: &quot;&quot;
}</pre>
</div>

<div id="default-vocabulary" class="section">
<h3><span class="secno">4.2 </span>Default Vocabulary</h3>
<p>It is often common that all types and properties come from the same vocabulary. JSON-LD provides
  a way to set a base URI to be used for all properties and types that aren't based on terms,
  prefixes or absolute IRIs. Much like the <code>@base</code> keyword, the <code>@vocab</code> keyword
  can be used to set a base <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a> to use for all types and properties that don't otherwise resolve to
  an absolute <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>.

</p><pre class="example">{
  <span class="diff">&quot;@context&quot;: { &quot;@vocab&quot;: &quot;http://xmlns.com/foaf/1.0/&quot; },</span>
  <span class="diff">&quot;@type&quot;: &quot;Person&quot;</span>,
  &quot;name&quot;: &quot;Manu Sporny&quot;,
  &quot;homepage&quot;: &quot;http://manu.sporny.org/&quot;,
  &quot;avatar&quot;: &quot;http://twitter.com/account/profile_image/manusporny&quot;
}</pre>
</div>

<div id="default-language" class="section">
<h3><span class="secno">4.3 </span>Default Language</h3>
<p>JSON-LD allows a default value to use as the language for <a class="tref internalDFN" title="plain_literal" href="#dfn-plain_literal">plain literal</a>s.
  It is commonly the case that documents are written using a single language. As described in
  <a href="string-internationalization">String Internationalization</a>, a language-tagged literal
  may be specified as follows:</p>

<pre class="example">{
...
  &quot;name&quot;:
  {
    &quot;@literal&quot;: &quot;花澄&quot;,
    &quot;@language&quot;: &quot;ja&quot;
  }
...
}</pre>

<p>By specifying <code>@language</code> within a <a class="tref internalDFN" title="context" href="#dfn-context">context</a>, multiple language-tagged literals may be
  marked up using a simple string form:</p>
</div>

<pre class="example">{
  <span class="diff">&quot;@context&quot;: { &quot;@language&quot;: &quot;ja&quot;}</span>,
...
  &quot;name&quot;: <span class="diff">&quot;花澄&quot;</span>
...
}</pre>
<div id="vocabulary-prefixes" class="section">
  <h3><span class="secno">4.4 </span>Vocabulary Prefixes</h3>
  <p>
    Vocabulary terms in <a class="tref internalDFN" title="linked_data" href="#dfn-linked_data">Linked Data</a> documents may draw from a number of
    different Web vocabularies. At times, declaring every single term that
    a document uses can require the developer to declare tens, if not
    hundreds of potential vocabulary terms that may be used across an
    application. This is a concern for at least three reasons; the
    first is the cognitive load on the developer, the second is
    the serialized size of the <a class="tref internalDFN" title="context" href="#dfn-context">context</a>, the third is future-proofing
    application contexts. In order to address these issues, the concept of a
    <a class="tref internalDFN" title="prefix" href="#dfn-prefix">prefix</a> mechanism is introduced.</p>
  <p>
    A <dfn title="prefix" id="dfn-prefix">prefix</dfn> is a compact way of expressing a base
    <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a> to a <a class="tref internalDFN" title="web_vocabulary" href="#dfn-web_vocabulary">Web Vocabulary</a>.
    Generally, these prefixes are used by concatenating the <em>prefix</em> and
    a <em>suffix</em> separated by a colon (<code>:</code>).
    The <a class="tref internalDFN" title="prefix" href="#dfn-prefix">prefix</a> is a <a class="tref internalDFN" title="term" href="#dfn-term">term</a> taken from the <a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a>,
    a short string that identifies a particular Web vocabulary.
    For example, the prefix <code>foaf</code> may be used as a short
    hand for the Friend-of-a-Friend Web Vocabulary, which is identified using
    the IRI <code>http://xmlns.com/foaf/0.1/</code>. A developer may append any of
    the FOAF Vocabulary terms to the end of the prefix to specify a short-hand
    version of the absolute IRI for the vocabulary term. For example,
    <code>foaf:name</code> would be expanded out to the IRI
    <code>http://xmlns.com/foaf/0.1/name</code>. Instead of having to remember
    and type out the entire IRI, the developer can instead use the prefix in
    their JSON-LD markup.
  </p>
  <p>
    The ability to use <a class="tref internalDFN" title="prefix" href="#dfn-prefix">prefix</a>es reduces the need for developers
    to declare every vocabulary term that they intend to use in
    the JSON-LD <a class="tref internalDFN" title="context" href="#dfn-context">context</a>. This reduces document serialization size because
    every vocabulary term need not be declared in the context.
    <a class="tref internalDFN" title="prefix" href="#dfn-prefix">Prefix</a> also
    reduce the cognitive load on the developer. It is far easier to
    remember <code>foaf:name</code> than it is to remember
    <code>http://xmlns.com/foaf/0.1/name</code>. The use of prefixes also
    ensures that a <a class="tref internalDFN" title="context" href="#dfn-context">context</a> document does not have to be updated in lock-step
    with an externally defined <a class="tref internalDFN" title="web_vocabulary" href="#dfn-web_vocabulary">Web Vocabulary</a>. Without prefixes, a developer
    would need to keep their application context terms in lock-step with an
    externally defined Web Vocabulary. Rather, by just declaring the
    Web Vocabulary prefix, one can use new terms as they're declared
    without having to update the application's JSON-LD <a class="tref internalDFN" title="context" href="#dfn-context">context</a>.
  </p>
  <p>Consider the following example:</p>
  <pre class="example">{
  &quot;@context&quot;: {
    <span class="diff">&quot;dc&quot;: &quot;http://purl.org/dc/elements/1.1/&quot;,</span>
    <span class="diff">&quot;ex&quot;: &quot;http://example.org/vocab#&quot;</span>
  },
  &quot;@subject&quot;: &quot;http://example.org/library&quot;,
  &quot;@type&quot;: <span class="diff">&quot;ex:Library&quot;</span>,
  <span class="diff">&quot;ex:contains&quot;</span>: {
    &quot;@subject&quot;: &quot;http://example.org/library/the-republic&quot;,
    &quot;@type&quot;: <span class="diff">&quot;ex:Book&quot;</span>,
    <span class="diff">&quot;dc:creator&quot;</span>: &quot;Plato&quot;,
    <span class="diff">&quot;dc:title&quot;</span>: &quot;The Republic&quot;,
    <span class="diff">&quot;ex:contains&quot;</span>: {
      &quot;@subject&quot;: &quot;http://example.org/library/the-republic#introduction&quot;,
      &quot;@type&quot;: <span class="diff">&quot;ex:Chapter&quot;</span>,
      <span class="diff">&quot;dc:description&quot;</span>: &quot;An introductory chapter on The Republic.&quot;,
      <span class="diff">&quot;dc:title&quot;</span>: &quot;The Introduction&quot;
    },
  },
}</pre>
  <p>
    In this example, two different vocabularies are referred to using
    prefixes. Those prefixes are then used as type and property values using
    the <code>prefix:suffix</code> notation.
  </p>
  <p>
    Prefixes, also known as CURIEs, are defined more formally in RDFa Core 1.1,
    <cite><a href="http://www.w3.org/TR/rdfa-core/#s_curies">Section 6
    &quot;CURIE Syntax Definition&quot;</a></cite> [<cite><a class="bibref" rel="biblioentry" href="#bib-RDFA-CORE">RDFA-CORE</a></cite>].
    JSON-LD does not support the square-bracketed CURIE syntax as the
    mechanism is not required to disambiguate <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>s in a JSON-LD document like
    it is in HTML documents.
  </p>
</div>

<div id="automatic-typing" class="section">
<h3><span class="secno">4.5 </span>Automatic Typing</h3>

<p>Since JSON is capable of expressing typed information such as doubles,
integers, and boolean values. As demonstrated below, JSON-LD utilizes that
information to create <a class="tref internalDFN" title="typed_literal" href="#dfn-typed_literal">typed literal</a>s:</p>

<pre class="example">{
...
  // The following two values are automatically converted to a type of xsd:double
  // and both values are equivalent to each other.
  &quot;measure:cups&quot;: <span class="diff">5.3</span>,
  &quot;measure:cups&quot;: <span class="diff">5.3e0</span>,
  // The following value is automatically converted to a type of xsd:double as well
  &quot;space:astronomicUnits&quot;: <span class="diff">6.5e73</span>,
  // The following value should never be converted to a language-native type
  &quot;measure:stones&quot;: <span class="diff">{ &quot;@literal&quot;: &quot;4.8&quot;, &quot;@datatype&quot;: &quot;xsd:decimal&quot; }</span>,
  // This value is automatically converted to having a type of xsd:integer
  &quot;chem:protons&quot;: <span class="diff">12</span>,
  // This value is automatically converted to having a type of xsd:boolean
  &quot;sensor:active&quot;: <span class="diff">true</span>,
...
}</pre>

<p class="note">When dealing with a number of modern programming languages,
including JavaScript ECMA-262, there is no distinction between
<strong>xsd:decimal</strong> and <strong>xsd:double</strong> values. That is,
the <a class="tref internalDFN" title="number" href="#dfn-number">number</a> <code>5.3</code> and the <a class="tref internalDFN" title="number" href="#dfn-number">number</a>
<code>5.3e0</code> are treated as if they were the same. When converting from
JSON-LD to a language-native format and back, datatype information is lost in a
number of these languages. Thus, one could say that <code>5.3</code> is a
<strong>xsd:decimal</strong> and <code>5.3e0</code> is an
<strong>xsd:double</strong> in JSON-LD, but when both values are
converted to a language-native format the datatype difference between the two
is lost because the machine-level representation will almost always be a
<strong>double</strong>.
Implementers should be aware of this potential round-tripping issue between
<strong>xsd:decimal</strong> and <strong>xsd:double</strong>. Specifically
objects with a datatype of <strong>xsd:decimal</strong> <em class="rfc2119" title="must not">must not</em> be converted
to a language native type.
</p>

</div>

<div id="type-coercion" class="section">
<h3><span class="secno">4.6 </span>Type Coercion</h3>

<p>JSON-LD supports the coercion of values to particular data types.
Type coercion allows someone deploying JSON-LD to coerce the incoming or
outgoing types to the proper data type based on a mapping of data type <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>s to
property types. Using type coercion, one may convert simple JSON data to
properly typed RDF data.</p>

<p>The example below demonstrates how a JSON-LD author can coerce values to
<a class="tref internalDFN" title="plain_literal" href="#dfn-plain_literal">plain literal</a>s, <a class="tref internalDFN" title="typed_literal" href="#dfn-typed_literal">typed literal</a>s and IRIs.</p>

<pre class="example">{
  &quot;@context&quot;:
  {
     &quot;rdf&quot;: &quot;http://www.w3.org/1999/02/22-rdf-syntax-ns#&quot;,
     &quot;xsd&quot;: &quot;http://www.w3.org/2001/XMLSchema#&quot;,
     &quot;name&quot;: &quot;http://xmlns.com/foaf/0.1/name&quot;,
     &quot;age&quot;: &quot;http://xmlns.com/foaf/0.1/age&quot;,
     &quot;homepage&quot;: &quot;http://xmlns.com/foaf/0.1/homepage&quot;,
<span class="diff">     &quot;@coerce&quot;:
     {
        &quot;xsd:integer&quot;: &quot;age&quot;,
        &quot;@iri&quot;: &quot;homepage&quot;
     }</span>
  },
  &quot;name&quot;: &quot;John Smith&quot;,
  &quot;age&quot;: <span class="diff">&quot;41&quot;</span>,
  &quot;homepage&quot;: <span class="diff">&quot;http://example.org/home/&quot;</span>
}</pre>

<p>The example above would generate the following triples:</p>

<pre class="example">_:bnode1
   &lt;http://xmlns.com/foaf/0.1/name&gt;
      &quot;John Smith&quot; .
_:bnode1
   &lt;http://xmlns.com/foaf/0.1/age&gt;
      &quot;41&quot;^^http://www.w3.org/2001/XMLSchema#integer .
_:bnode1
   &lt;http://xmlns.com/foaf/0.1/homepage&gt;
      &lt;http://example.org/home/&gt; .</pre>

<div class="issue">
  <p>The mechanism for type coercion is still being debated. It may be that the key/value
    positions are swapped, yielding a <code>@context</code> such as the following:</p>

<pre class="example">{
  &quot;@context&quot;: {
    &quot;rdf&quot;: &quot;http://www.w3.org/1999/02/22-rdf-syntax-ns#&quot;,
    &quot;xsd&quot;: &quot;http://www.w3.org/2001/XMLSchema#&quot;,
    &quot;name&quot;: &quot;http://xmlns.com/foaf/0.1/name&quot;,
    &quot;age&quot;: &quot;http://xmlns.com/foaf/0.1/age&quot;,
    &quot;homepage&quot;: &quot;http://xmlns.com/foaf/0.1/homepage&quot;,
    &quot;currentProject&quot;: &quot;http://xmlns.com/foaf/0.1/currentProject&quot;,
    <span class="diff">&quot;@coerce&quot;: {
      &quot;age&quot;: &quot;xsd:integer&quot;,
      &quot;homepage&quot;: &quot;@iri&quot;,
      &quot;currentProject&quot;: [&quot;@iri&quot;, &quot;@list&quot;]
     }</span>
  },
  ...
}</pre>

<p>An alternative is to merge the coercion into term definitions:</p>

<pre class="example">{
  &quot;@context&quot;:
  {
    &quot;rdf&quot;: &quot;http://www.w3.org/1999/02/22-rdf-syntax-ns#&quot;,
    &quot;xsd&quot;: &quot;http://www.w3.org/2001/XMLSchema#&quot;,
    &quot;name&quot;: &quot;http://xmlns.com/foaf/0.1/name&quot;,
    &quot;age&quot;: <span class="diff">{&quot;@iri&quot;: &quot;http://xmlns.com/foaf/0.1/age&quot;, &quot;@coerce&quot;: &quot;xsd:integer&quot;}</span>,
    &quot;homepage&quot;: <span class="diff">{&quot;@iri&quot;: &quot;http://xmlns.com/foaf/0.1/age&quot;, &quot;@coerce&quot;: &quot;@iri&quot;}</span>,
    &quot;currentProject&quot;: <span class="diff">{&quot;@iri&quot;: &quot;http://xmlns.com/foaf/0.1/currentProject&quot;, &quot;@coerce&quot;: [&quot;@iri&quot;, &quot;@list&quot;]}</span>,
  },
  ...
}</pre>
</div>

</div>

<div id="chaining" class="section">
  <h3><span class="secno">4.7 </span>Chaining</h3>
  <p>
    Object <dfn title="chaining" id="dfn-chaining">chaining</dfn> is a JSON-LD feature that allows an author to
    use the definition of JSON-LD objects as <a class="tref internalDFN" title="property" href="#dfn-property">property</a> values. This
    is a commonly used mechanism for creating a parent-child relationship
    between two <a class="tref internalDFN" title="subject" href="#dfn-subject">subject</a>s.
  </p>
  <p>The example shows an two subjects related by a property from the first
  subject:</p>

  <pre class="example">{
...
  &quot;name&quot;: &quot;Manu Sporny&quot;,
  &quot;<span class="diff">knows</span>&quot;: {
    &quot;<span class="diff">@type</span>&quot;: &quot;<span class="diff">Person</span>&quot;,
    &quot;<span class="diff">name</span>&quot;: &quot;<span class="diff">Gregg Kellogg</span>&quot;,
  }
...
}</pre>

  <p>
    An object definition, like the one used above, <em class="rfc2119" title="may">may</em> be used as a
    JSON value at any point in JSON-LD.
  </p>
</div>

<div id="identifying-unlabeled-nodes" class="section">
<h3><span class="secno">4.8 </span>Identifying Unlabeled Nodes</h3>

<p>At times, it becomes necessary to be able to express information without
being able to specify the subject. Typically, this type of node is called
an unlabeled node or a blank node. In JSON-LD, unlabeled node identifiers are
automatically created if a subject is not specified using the
<code>@subject</code> keyword. However, authors may provide identifiers for
unlabeled nodes by using the special <code>_</code> (underscore)
<a class="tref internalDFN" title="prefix" href="#dfn-prefix">prefix</a>. This allows to reference the node locally within the
document but not in an external document.</p>

<pre class="example">{
...
  &quot;@subject&quot;: &quot;<span class="diff">_:foo</span>&quot;,
...
}</pre>

<p>The example above would set the subject to <code>_:foo</code>, which can
then be used later on in the JSON-LD markup to refer back to the
unlabeled node. This practice, however, is usually frowned upon when
generating <a class="tref internalDFN" title="linked_data" href="#dfn-linked_data">Linked Data</a>. If a developer finds that they refer to the unlabeled
node more than once, they should consider naming the node using a resolve-able
<a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>.
</p>

</div>

<div id="aliasing-keywords" class="section">
<h3><span class="secno">4.9 </span>Aliasing Keywords</h3>

<p>JSON-LD allows all of the syntax keywords, except for <code>@context</code>,
to be aliased. This feature allows more legacy JSON content to be supported
by JSON-LD. It also allows developers to design domain-specific implementations
using only the JSON-LD <a class="tref internalDFN" title="context" href="#dfn-context">context</a>.</p>

<pre class="example">{
  &quot;@context&quot;:
  {
     <span class="diff">&quot;url&quot;: &quot;@subject&quot;</span>,
     <span class="diff">&quot;a&quot;: &quot;@type&quot;</span>,
     &quot;name&quot;: &quot;http://schema.org/name&quot;
  },
  &quot;url&quot;: &quot;http://example.com/about#gregg&quot;,
  &quot;a&quot;: &quot;http://schema.org/Person&quot;,
  &quot;name&quot;: &quot;Gregg Kellogg&quot;
}</pre>

<p>In the example above, the <code>@subject</code> and <code>@type</code>
keywords have been given the aliases <strong>url</strong> and
<strong>a</strong>, respectively.
</p>

</div>

</div>

<div id="using-json-ld-for-rdf" class="section">
  
<!-- OddPage -->
<h2><span class="secno">5. </span>Using JSON-LD for RDF</h2>

  <p>JSON-LD is a specification for representing <a class="tref internalDFN" title="linked_data" href="#dfn-linked_data">Linked Data</a> in JSON. A common
    way of working with Linked Data is through <dfn title="rdf" id="dfn-rdf">RDF</dfn>, the Resource Description Framework.
    RDF can be expressed using JSON-LD by associating JSON-LD concepts such as <code>@subject</code>
    and <code>@type</code> with the equivalent <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>s in RDF. Further information about
    RDF may be found in [<cite><a class="bibref" rel="biblioentry" href="#bib-RDF-PRIMER">RDF-PRIMER</a></cite>].</p>

  <p>Some examples of encoding <a class="tref internalDFN" title="rdf" href="#dfn-rdf">RDF</a> into JSON-LD may be found
    in <a href="#markup-examples">Appendix A</a>. Details of transforming JSON-LD into RDF
    are defined in [<cite><a class="bibref" rel="biblioentry" href="#bib-JSON-LD-API">JSON-LD-API</a></cite>].</p>
</div>

<div class="appendix section" id="markup-examples">

<!-- OddPage -->
<h2><span class="secno">A. </span>Markup Examples</h2>

<p>The JSON-LD markup examples below demonstrate how JSON-LD can be used to
  express semantic data marked up in other languages such as RDFa, Microformats,
  and Microdata. These sections are merely provided as proof that JSON-LD is
  very flexible in what it can express across different <a class="tref internalDFN" title="linked_data" href="#dfn-linked_data">Linked Data</a> approaches.</p>

<div id="turtle" class="section">
  <h3><span class="secno">A.1 </span>Turtle</h3>
  
  <p>The following are examples of representing <a class="tref internalDFN" title="rdf" href="#dfn-rdf">RDF</a> as expressed in [<cite><a class="bibref" rel="biblioentry" href="#bib-TURTLE">TURTLE</a></cite>] into JSON-LD.</p>
  
<div id="prefix-and-base-definitions" class="section">
<h4><span class="secno">A.1.1 </span>Prefix and Base definitions</h4>
<p>The JSON-LD context has direct equivalents for Turtle <code>@base</code> and <code>@prefix</code> expressions:</p>

<pre class="example">@base &lt;http://manu.sporny.org/&gt; .
@prefix foaf: &lt;http://xmlns.com/foaf/0.1/&gt; .

&lt;#me&gt; a foaf:Person;
  foaf:name &quot;Manu Sporny&quot;;
  foaf:homepage &lt;&gt; .</pre>

<pre class="example">{
  &quot;@context&quot;: {
    &quot;@base&quot;:  &quot;http://manu.sporny.org/&quot;,
    &quot;foaf&quot;:   &quot;http://xmlns.com/foaf/0.1/&quot;
  },
  &quot;@subject&quot;:       &quot;#me&quot;,
  &quot;@type&quot;:          &quot;foaf:Person&quot;,
  &quot;foaf:name&quot;:      &quot;Manu Sporny&quot;,
  &quot;foaf:homepage&quot;:  {&quot;@iri&quot;: &quot;&quot;}
}</pre>
</div>

<div id="chaining-1" class="section">
<h4><span class="secno">A.1.2 </span>Chaining</h4>
<p>Both Turtle and JSON-LD allow chaining of objects, although Turtle only allows chaining of objects which
  use nlank node identifiers.</p>
</div>

<pre class="example">@base &lt;http://manu.sporny.org/&gt; .
@prefix foaf: &lt;http://xmlns.com/foaf/0.1/&gt; .

&lt;#me&gt; a foaf:Person;
  foaf:name &quot;Manu Sporny&quot;;
  foaf:knows [ a foaf:Person; foaf:name &quot;Gregg Kellogg&quot; ] .</pre>

<pre class="example">{
  &quot;@context&quot;: {
    &quot;@base&quot;:  &quot;http://manu.sporny.org/&quot;,
    &quot;foaf&quot;:   &quot;http://xmlns.com/foaf/0.1/&quot;
  },
  &quot;@subject&quot;:       &quot;#me&quot;,
  &quot;@type&quot;:          &quot;foaf:Person&quot;,
  &quot;foaf:name&quot;:      &quot;Manu Sporny&quot;,
  &quot;foaf:knows&quot;:  {
    &quot;@type&quot;:          &quot;foaf:Person&quot;,
    &quot;foaf:name&quot;:      &quot;Gregg Kellogg&quot;
  }
}</pre>
<div id="lists-1" class="section">
<h4><span class="secno">A.1.3 </span>Lists</h4>
<p>Both JSON-LD and Turtle can represent sequential lists of values.</p>

<pre class="example">@prefix foaf: &lt;http://xmlns.com/foaf/0.1/&gt; .

&lt;http://example.org/people#joebob&gt; a foaf:Person;
  foaf:name &quot;Joe Bob&quot;;
  foaf:nick ( &quot;joe&quot; &quot;bob&quot; &quot;jaybee&quot;) .</pre>

<pre class="example">{
  &quot;@context&quot;: {
    &quot;@base&quot;:  &quot;http://manu.sporny.org/&quot;,
    &quot;foaf&quot;:   &quot;http://xmlns.com/foaf/0.1/&quot;
  },
  &quot;@subject&quot;:       &quot;http://example.org/people#joebob&quot;,
  &quot;@type&quot;:          &quot;foaf:Person&quot;,
  &quot;foaf:name&quot;:      &quot;Joe Bob&quot;,
  &quot;foaf:nick&quot;:      {&quot;@list&quot;: [&quot;joe&quot;, &quot;bob&quot;, &quot;jaybe&quot;]}
}</pre>
</div>

</div>

<div id="rdfa" class="section">
<h3><span class="secno">A.2 </span>RDFa</h3>

<p>The following example describes three people with their respective names and
homepages.</p>

<pre class="example">&lt;div <span class="diff">prefix=&quot;foaf: http://xmlns.com/foaf/0.1/&quot;</span>&gt;
   &lt;ul&gt;
      &lt;li <span class="diff">typeof=&quot;foaf:Person&quot;</span>&gt;
        &lt;a <span class="diff">rel=&quot;foaf:homepage&quot; href=&quot;http://example.com/bob/&quot; property=&quot;foaf:name&quot; </span>&gt;Bob&lt;/a&gt;
      &lt;/li&gt;
      &lt;li <span class="diff">typeof=&quot;foaf:Person&quot;</span>&gt;
        &lt;a <span class="diff">rel=&quot;foaf:homepage&quot; href=&quot;http://example.com/eve/&quot; property=&quot;foaf:name&quot; </span>&gt;Eve&lt;/a&gt;
      &lt;/li&gt;
      &lt;li <span class="diff">typeof=&quot;foaf:Person&quot;</span>&gt;
        &lt;a <span class="diff">rel=&quot;foaf:homepage&quot; href=&quot;http://example.com/manu/&quot; property=&quot;foaf:name&quot; </span>&gt;Manu&lt;/a&gt;
      &lt;/li&gt;
   &lt;/ul&gt;
&lt;/div&gt;</pre>

<p>An example JSON-LD implementation is described below, however, there are
other ways to mark-up this information such that the <a class="tref internalDFN" title="context" href="#dfn-context">context</a> is not
repeated.</p>

<pre class="example">{
  &quot;@context&quot;: { &quot;foaf&quot;: &quot;http://xmlns.com/foaf/0.1/&quot;},
  &quot;@subject&quot;: [
   {
     &quot;@subject&quot;: &quot;_:bnode1&quot;,
     &quot;@type&quot;: &quot;foaf:Person&quot;,
     &quot;foaf:homepage&quot;: &quot;http://example.com/bob/&quot;,
     &quot;foaf:name&quot;: &quot;Bob&quot;
   },
   {
     &quot;@subject&quot;: &quot;_:bnode2&quot;,
     &quot;@type&quot;: &quot;foaf:Person&quot;,
     &quot;foaf:homepage&quot;: &quot;http://example.com/eve/&quot;,
     &quot;foaf:name&quot;: &quot;Eve&quot;
   },
   {
     &quot;@subject&quot;: &quot;_:bnode3&quot;,
     &quot;@type&quot;: &quot;foaf:Person&quot;,
     &quot;foaf:homepage&quot;: &quot;http://example.com/manu/&quot;,
     &quot;foaf:name&quot;: &quot;Manu&quot;
   }
  ]
}</pre>

</div>

<div id="microformats" class="section">
<h3><span class="secno">A.3 </span>Microformats</h3>

<p>The following example uses a simple Microformats hCard example to express
how the Microformat is represented in JSON-LD.</p>

<pre class="example">&lt;div class=&quot;vcard&quot;&gt;
 &lt;a class=&quot;url fn&quot; href=&quot;http://tantek.com/&quot;&gt;Tantek Çelik&lt;/a&gt;
&lt;/div&gt;</pre>

<p>The representation of the hCard expresses the Microformat terms in the
<a class="tref internalDFN" title="context" href="#dfn-context">context</a> and uses them directly for the <code>url</code> and <code>fn</code>
properties. Also note that the Microformat to JSON-LD processor has
generated the proper URL type for <code>http://tantek.com</code>.</p>

<pre class="example">{
  &quot;@context&quot;:
  {
    &quot;vcard&quot;: &quot;http://microformats.org/profile/hcard#vcard&quot;,
    &quot;url&quot;: &quot;http://microformats.org/profile/hcard#url&quot;,
    &quot;fn&quot;: &quot;http://microformats.org/profile/hcard#fn&quot;,
    &quot;@coerce&quot;: { &quot;@iri&quot;: &quot;url&quot; }
  },
  &quot;@subject&quot;: &quot;_:bnode1&quot;,
  &quot;@type&quot;: &quot;vcard&quot;,
  &quot;url&quot;: &quot;http://tantek.com/&quot;,
  &quot;fn&quot;: &quot;Tantek Çelik&quot;
}</pre>

</div>

<div id="microdata" class="section">
<h3><span class="secno">A.4 </span>Microdata</h3>

<p>The Microdata example below expresses book information as a Microdata Work
item.
</p>

<pre class="example">&lt;dl itemscope
    itemtype=&quot;http://purl.org/vocab/frbr/core#Work&quot;
    itemid=&quot;http://purl.oreilly.com/works/45U8QJGZSQKDH8N&quot;&gt;
 &lt;dt&gt;Title&lt;/dt&gt;
 &lt;dd&gt;&lt;cite itemprop=&quot;http://purl.org/dc/terms/title&quot;&gt;Just a Geek&lt;/cite&gt;&lt;/dd&gt;
 &lt;dt&gt;By&lt;/dt&gt;
 &lt;dd&gt;&lt;span itemprop=&quot;http://purl.org/dc/terms/creator&quot;&gt;Wil Wheaton&lt;/span&gt;&lt;/dd&gt;
 &lt;dt&gt;Format&lt;/dt&gt;
 &lt;dd itemprop=&quot;http://purl.org/vocab/frbr/core#realization&quot;
     itemscope
     itemtype=&quot;http://purl.org/vocab/frbr/core#Expression&quot;
     itemid=&quot;http://purl.oreilly.com/products/9780596007683.BOOK&quot;&gt;
  &lt;link itemprop=&quot;http://purl.org/dc/terms/type&quot; href=&quot;http://purl.oreilly.com/product-types/BOOK&quot;&gt;
  Print
 &lt;/dd&gt;
 &lt;dd itemprop=&quot;http://purl.org/vocab/frbr/core#realization&quot;
     itemscope
     itemtype=&quot;http://purl.org/vocab/frbr/core#Expression&quot;
     itemid=&quot;http://purl.oreilly.com/products/9780596802189.EBOOK&quot;&gt;
  &lt;link itemprop=&quot;http://purl.org/dc/terms/type&quot; href=&quot;http://purl.oreilly.com/product-types/EBOOK&quot;&gt;
  Ebook
 &lt;/dd&gt;
&lt;/dl&gt;</pre>

<p>Note that the JSON-LD representation of the Microdata information stays
true to the desires of the Microdata community to avoid contexts and
instead refer to items by their full <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>.</p>

<pre class="example">[
  {
    &quot;@subject&quot;: &quot;http://purl.oreilly.com/works/45U8QJGZSQKDH8N&quot;,
    &quot;@type&quot;: &quot;http://purl.org/vocab/frbr/core#Work&quot;,
    &quot;http://purl.org/dc/terms/title&quot;: &quot;Just a Geek&quot;,
    &quot;http://purl.org/dc/terms/creator&quot;: &quot;Whil Wheaton&quot;,
    &quot;http://purl.org/vocab/frbr/core#realization&quot;:
      [&quot;http://purl.oreilly.com/products/9780596007683.BOOK&quot;, &quot;http://purl.oreilly.com/products/9780596802189.EBOOK&quot;]
  },
  {
    &quot;@subject&quot;: &quot;http://purl.oreilly.com/products/9780596007683.BOOK&quot;,
    &quot;@type&quot;: &quot;http://purl.org/vocab/frbr/core#Expression&quot;,
    &quot;http://purl.org/dc/terms/type&quot;: &quot;http://purl.oreilly.com/product-types/BOOK&quot;
  },
  {
    &quot;@subject&quot;: &quot;http://purl.oreilly.com/products/9780596802189.EBOOK&quot;,
    &quot;@type&quot;: &quot;http://purl.org/vocab/frbr/core#Expression&quot;,
    &quot;http://purl.org/dc/terms/type&quot;: &quot;http://purl.oreilly.com/product-types/EBOOK&quot;
  }
]</pre>
</div>
</div>

<div class="appendix section" id="mashing-up-vocabularies">

<!-- OddPage -->
<h2><span class="secno">B. </span>Mashing Up Vocabularies</h2>

<p>Developers would also benefit by allowing other vocabularies to be used
automatically with their JSON API. There are over 200
<a class="tref internalDFN" title="web_vocabulary" href="#dfn-web_vocabulary">Web Vocabulary</a> Documents that are available for use on the Web
today. Some of these vocabularies are:
</p>

<ul>
   <li>RDF - for describing information about objects and concepts on the Web.</li>
   <li>RDFS - for expressing things like labels and comments.</li>
   <li>XSD - for specifying basic types like strings, integers, dates and times.</li>
   <li>Dublin Core - for describing creative works.</li>
   <li>FOAF - for describing social networks.</li>
   <li>Calendar - for specifying events.</li>
   <li>SIOC - for describing discussions on blogs and websites.</li>
   <li>CCrel - for describing Creative Commons and other types of licenses.</li>
   <li>GEO - for describing geographic location.</li>
   <li>VCard - for describing organizations and people.</li>
   <li>DOAP - for describing projects.</li>
</ul>

<p>You can use these vocabularies in combination, like so:</p>

<pre class="example">{
  &quot;<span class="diff">@type</span>&quot;: &quot;<span class="diff">foaf:Person</span>&quot;,
  &quot;<span class="diff">foaf:name</span>&quot;: &quot;Manu Sporny&quot;,
  &quot;<span class="diff">foaf:homepage</span>&quot;: &quot;http://manu.sporny.org/&quot;,
  &quot;<span class="diff">sioc:avatar</span>&quot;: &quot;http://twitter.com/account/profile_image/manusporny&quot;
}</pre>

<p>Developers can also specify their own Vocabulary documents by modifying the
<a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a> in-line using the <code>@context</code> keyword,
like so:</p>

<pre class="example">{
  <span class="diff">&quot;@context&quot;: { &quot;myvocab&quot;: &quot;http://example.org/myvocab#&quot; }</span>,
  &quot;@type&quot;: &quot;foaf:Person&quot;,
  &quot;foaf:name&quot;: &quot;Manu Sporny&quot;,
  &quot;foaf:homepage&quot;: &quot;http://manu.sporny.org/&quot;,
  &quot;sioc:avatar&quot;: &quot;http://twitter.com/account/profile_image/manusporny&quot;<span class="diff">,
  &quot;myvocab:personality&quot;: &quot;friendly&quot;</span>
}</pre>

<p>The <code>@context</code> keyword is used to change how the JSON-LD
processor evaluates key-value pairs. In this case, it was used to
map one string ('myvocab') to another string, which is interpreted as
a <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>. In the example above, the <code>myvocab</code> string is replaced
with &quot;<code>http://example.org/myvocab#</code>&quot; when it
is detected. In the example above, &quot;<code>myvocab:personality</code>&quot; would
expand to &quot;<code>http://example.org/myvocab#personality</code>&quot;.</p>

<p>This mechanism is a short-hand, called a <a class="tref internalDFN" title="web_vocabulary" href="#dfn-web_vocabulary">Web Vocabulary</a> <a class="tref internalDFN" title="prefix" href="#dfn-prefix">prefix</a>,
and provides developers an unambiguous way to map any JSON value to RDF.</p><p>

</p></div>

<div class="appendix section" id="iana-considerations">

<!-- OddPage -->
<h2><span class="secno">C. </span>IANA Considerations</h2>

<p>This section is included merely for standards community review and will be
submitted to the Internet Engineering Steering Group if this specification
becomes a W3C Recommendation.</p>

<dl>
  <dt>Type name:</dt>
  <dd>application</dd>
  <dt>Subtype name:</dt>
  <dd>ld+json</dd>
  <dt>Required parameters:</dt>
  <dd>None</dd>
  <dt>Optional parameters:</dt>
  <dd>
    <dl>
      <dt><code>form</code></dt>
      <dd>Determines the serialization form for the JSON-LD document. Valid
        values include; <code>compacted</code>, <code>expanded</code>,
        <code>framed</code>, and <code>normalized</code>. Other values are
        allowed, but must be pre-pended with a <code>x-</code> string until
        they are clearly defined by a stable specification. If no form
        is specified in an HTTP request header to a responding application,
        such as a Web server, the application <em class="rfc2119" title="may">may</em> choose any form. If no
        form is specified for a receiving application, the form <em class="rfc2119" title="must not">must not</em>
        be assumed to take any particular form.</dd>
      <div class="issue">It is currently <a href="https://github.com/json-ld/json-ld.org/issues/14"> being discussed to remove form=framed</a> from this specification as there are several issues with it.</div>
    </dl>
  </dd>
  <dt>Encoding considerations:</dt>
  <dd>The same as the <code>application/json</code> MIME media type.</dd>
  <dt>Security considerations:</dt>
  <dd>Since JSON-LD is intended to be a pure data exchange format for
    directed graphs, the serialization <em class="rfc2119" title="should not">should not</em> be passed through a
    code execution mechanism such as JavaScript's <code>eval()</code>
    function. It is <em class="rfc2119" title="recommended">recommended</em> that a conforming parser does not attempt to
    directly evaluate the JSON-LD serialization and instead purely parse the
    input into a language-native data structure. </dd>
  <dt>Interoperability considerations:</dt>
  <dd>Not Applicable</dd>
  <dt>Published specification:</dt>
  <dd>The <a href="http://json-ld/spec/latest/">JSON-LD</a> specification.</dd>
  <dt>Applications that use this media type:</dt>
  <dd>Any programming environment that requires the exchange of
    directed graphs. Implementations of JSON-LD have been created for
    JavaScript, Python, Ruby, PHP and C++.
  </dd>
  <dt>Additional information:</dt>
  <dd>
    <dl>
      <dt>Magic number(s):</dt>
      <dd>Not Applicable</dd>
      <dt>File extension(s):</dt>
      <dd>.jsonld</dd>
      <dt>Macintosh file type code(s):</dt>
      <dd>TEXT</dd>
    </dl>
  </dd>
  <dt>Person &amp; email address to contact for further information:</dt>
  <dd>Manu Sporny &lt;msporny@digitalbazaar.com&gt;</dd>
  <dt>Intended usage:</dt>
  <dd>Common</dd>
  <dt>Restrictions on usage:</dt>
  <dd>None</dd>
  <dt>Author(s):</dt>
  <dd>Manu Sporny, Gregg Kellogg, Dave Longley</dd>
  <dt>Change controller:</dt>
  <dd>W3C</dd>
</dl>

</div>

<div class="appendix section" id="acknowledgements">

<!-- OddPage -->
<h2><span class="secno">D. </span>Acknowledgements</h2>

<p>The editors would like to thank Mark Birbeck, who provided a great deal of
the initial push behind the JSON-LD work via his work on RDFj,
Dave Longley, Dave Lehn and Mike Johnson who reviewed, provided feedback, and
performed several implementations of the specification, and Ian Davis, who
created RDF/JSON. Thanks also to Nathan Rixham, Bradley P. Allen,
Kingsley Idehen, Glenn McDonald, Alexandre Passant, Danny Ayers, Ted
Thibodeau Jr., Olivier Grisel, Niklas Lindström, Markus Lanthaler, and Richard
Cyganiak for their input on the specification.
</p>
</div>



<div id="respec-err" style="position: fixed; width: 350px; top: 10px; right: 10px; border: 3px double #f00; background: #fff" class="removeOnSave"><ul><li style="color: #c00">There appears to have been a problem fetching the style sheet; status=0</li></ul></div><div id="references" class="appendix section">
<!-- OddPage -->
<h2><span class="secno">E. </span>References</h2><div id="normative-references" class="section"><h3><span class="secno">E.1 </span>Normative references</h3><dl class="bibliography"><dt id="bib-BCP47">[BCP47]</dt><dd>A. Phillips, M. Davis. <a href="http://tools.ietf.org/rfc/bcp/bcp47.txt"><cite>Tags for Identifying Languages</cite></a> September 2009. IETF Best Current Practice. URL: <a href="http://tools.ietf.org/rfc/bcp/bcp47.txt">http://tools.ietf.org/rfc/bcp/bcp47.txt</a>
</dd><dt id="bib-RDF-CONCEPTS">[RDF-CONCEPTS]</dt><dd>Graham Klyne; Jeremy J. Carroll. <a href="http://www.w3.org/TR/2004/REC-rdf-concepts-20040210"><cite>Resource Description Framework (RDF): Concepts and Abstract Syntax.</cite></a> 10 February 2004. W3C Recommendation. URL: <a href="http://www.w3.org/TR/2004/REC-rdf-concepts-20040210">http://www.w3.org/TR/2004/REC-rdf-concepts-20040210</a> 
</dd><dt id="bib-RFC3987">[RFC3987]</dt><dd>M. Dürst; M. Suignard. <a href="http://www.ietf.org/rfc/rfc3987.txt"><cite>Internationalized Resource Identifiers (IRIs).</cite></a> January 2005. Internet RFC 3987. URL: <a href="http://www.ietf.org/rfc/rfc3987.txt">http://www.ietf.org/rfc/rfc3987.txt</a> 
</dd><dt id="bib-RFC4627">[RFC4627]</dt><dd>D. Crockford. <a href="http://www.ietf.org/rfc/rfc4627.txt"><cite>The application/json Media Type for JavaScript Object Notation (JSON)</cite></a> July 2006. Internet RFC 4627. URL: <a href="http://www.ietf.org/rfc/rfc4627.txt">http://www.ietf.org/rfc/rfc4627.txt</a>
</dd><dt id="bib-WEBIDL">[WEBIDL]</dt><dd>Cameron McCormack. <a href="http://www.w3.org/TR/2008/WD-WebIDL-20081219"><cite>Web IDL.</cite></a> 19 December 2008. W3C Working Draft. (Work in progress.) URL: <a href="http://www.w3.org/TR/2008/WD-WebIDL-20081219">http://www.w3.org/TR/2008/WD-WebIDL-20081219</a> 
</dd></dl></div><div id="informative-references" class="section"><h3><span class="secno">E.2 </span>Informative references</h3><dl class="bibliography"><dt id="bib-ECMA-262">[ECMA-262]</dt><dd><a href="http://www.ecma-international.org/publications/standards/Ecma-262.htm"><cite>ECMAScript Language Specification, Third Edition.</cite></a> December 1999. URL: <a href="http://www.ecma-international.org/publications/standards/Ecma-262.htm">http://www.ecma-international.org/publications/standards/Ecma-262.htm</a> 
</dd><dt id="bib-HTML-RDFA">[HTML-RDFA]</dt><dd>Manu Sporny; et al. <a href="http://www.w3.org/TR/rdfa-in-html/"><cite>HTML+RDFa</cite></a> 04 March 2010. W3C Working Draft. URL: <a href="http://www.w3.org/TR/rdfa-in-html/">http://www.w3.org/TR/rdfa-in-html/</a> 
</dd><dt id="bib-JSON-LD-API">[JSON-LD-API]</dt><dd>Manu Sporny, Gregg Kellogg, Dave Longley, Eds. <cite><a href="http://json-ld.org/spec/latest/json-ld-api/">JSON-LD API</a></cite> Latest. W3C Editor's Draft. URL: <a href="http://json-ld.org/spec/latest/json-ld-api/">http://www.w3.org/2010/02/rdfa/sources/rdf-interfaces/</a>
</dd><dt id="bib-MICRODATA">[MICRODATA]</dt><dd>Ian Hickson; et al. <a href="http://www.w3.org/TR/microdata/"><cite>Microdata</cite></a> 04 March 2010. W3C Working Draft. URL: <a href="http://www.w3.org/TR/microdata/">http://www.w3.org/TR/microdata/</a> 
</dd><dt id="bib-MICROFORMATS">[MICROFORMATS]</dt><dd><a href="http://microformats.org"><cite>Microformats</cite></a>. URL: <a href="http://microformats.org">http://microformats.org</a> 
</dd><dt id="bib-RDF-PRIMER">[RDF-PRIMER]</dt><dd>Frank Manola; Eric Miller. <a href="http://www.w3.org/TR/2004/REC-rdf-primer-20040210/"><cite>RDF Primer.</cite></a> 10 February 2004. W3C Recommendation. URL: <a href="http://www.w3.org/TR/2004/REC-rdf-primer-20040210/">http://www.w3.org/TR/2004/REC-rdf-primer-20040210/</a> 
</dd><dt id="bib-RDF-SCHEMA">[RDF-SCHEMA]</dt><dd>Dan Brickley; Ramanathan V. Guha. <a href="http://www.w3.org/TR/2004/REC-rdf-schema-20040210"><cite>RDF Vocabulary Description Language 1.0: RDF Schema.</cite></a> 10 February 2004. W3C Recommendation. URL: <a href="http://www.w3.org/TR/2004/REC-rdf-schema-20040210">http://www.w3.org/TR/2004/REC-rdf-schema-20040210</a> 
</dd><dt id="bib-RDFA-CORE">[RDFA-CORE]</dt><dd>Shane McCarron; et al. <a href="http://www.w3.org/TR/2011/WD-rdfa-core-20110331"><cite>RDFa Core 1.1: Syntax and processing rules for embedding RDF through attributes.</cite></a> 31 March   <?xml version='1.0' encoding='UTF-8'?>
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  <meta http-equiv="content-type" content="text/html; charset=UTF-8" />

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  <body style="display: inherit; "><div class="head"><p></p><h1 class="title" id="title">JSON-LD Syntax 1.0</h1><h2 id="subtitle">A Context-based JSON Serialization for Linking Data</h2><h2 id="unofficial-draft-24-october-2011">Unofficial Draft 24 October 2011</h2><dl><dt>Editor:</dt><dd><a href="http://manu.sporny.org/">Manu Sporny</a>, <a href="http://digitalbazaar.com/">Digital Bazaar</a></dd>
  <dt>Authors:</dt><dd><a href="http://digitalbazaar.com/">Manu Sporny</a>, <a href="http://digitalbazaar.com/">Digital Bazaar</a></dd>
  <dd><a href="http://digitalbazaar.com/">Dave Longley</a>, <a href="http://digitalbazaar.com/">Digital Bazaar</a></dd>
  <dd><a href="http://greggkellogg.net/">Gregg Kellogg</a>, <a href="http://kellogg-assoc.com/">Kellogg Associates</a></dd>
  <dd><a href="http://www.markus-lanthaler.com/">Markus Lanthaler</a>, <a href="http://www.tugraz.at/">Graz University of Technology</a></dd>
  <dd><a href="http://webbackplane.com/">Mark Birbeck</a>, <a href="http://webbackplane.com/">Backplane Ltd.</a></dd>
  </dl><p>This document is also available in this non-normative format: <a href="diff-20111016.html">diff to previous version</a>.</p><p class="copyright">This document is licensed under a <a class="subfoot" href="http://creativecommons.org/licenses/by/3.0/" rel="license">Creative Commons Attribution 3.0 License</a>.</p><hr /></div>
  <div id="abstract" class="introductory section"><h2>Abstract</h2>
  <p>
  JSON [<cite><a class="bibref" rel="biblioentry" href="#bib-RFC4627">RFC4627</a></cite>] has proven to be a highly useful object serialization and
  messaging format. In an attempt to harmonize the representation of <a class="tref internalDFN" title="linked_data" href="#dfn-linked_data">Linked Data</a>
  in JSON, this specification outlines a common JSON representation format for
  expressing directed graphs; mixing both Linked Data and non-Linked Data in
  a single document.
  </p>
  </div><div id="sotd" class="introductory section"><h2>Status of This Document</h2><p>This document is merely a public working draft of a potential specification. It has no official standing of any kind and does not represent the support or consensus of any standards organisation.</p>
  <p>This document is an experimental work in progress.</p>

  <!--  <p>
  This document has been reviewed by W3C Members, by software
  developers, and by other W3C groups and interested parties, and is
  endorsed by the Director as a W3C Recommendation. It is a stable
  document and may be used as reference material or cited from another
  document. W3C's role in making the Recommendation is to draw attention
  to the specification and to promote its widespread deployment. This
  enhances the functionality and interoperability of the Web.
  </p>  -->

  </div><div id="toc" class="section"><h2 class="introductory">Table of Contents</h2><ul class="toc"><li class="tocline"><a href="#introduction" class="tocxref"><span class="secno">1. </span>Introduction</a><ul class="toc"><li class="tocline"><a href="#how-to-read-this-document" class="tocxref"><span class="secno">1.1 </span>How to Read this Document</a></li><li class="tocline"><a href="#syntax-tokens-and-keywords" class="tocxref"><span class="secno">1.2 </span>Syntax Tokens and Keywords</a></li><li class="tocline"><a href="#contributing" class="tocxref"><span class="secno">1.3 </span>Contributing</a></li></ul></li><li class="tocline"><a href="#design" class="tocxref"><span class="secno">2. </span>Design</a><ul class="toc"><li class="tocline"><a href="#goals-and-rationale" class="tocxref"><span class="secno">2.1 </span>Goals and Rationale</a></li><li class="tocline"><a href="#linked-data" class="tocxref"><span class="secno">2.2 </span>Linked Data</a></li><li class="tocline"><a href="#linking-data" class="tocxref"><span class="secno">2.3 </span>Linking Data</a></li><li class="tocline"><a href="#the-context" class="tocxref"><span class="secno">2.4 </span>The Context</a><ul class="toc"><li class="tocline"><a href="#external-contexts" class="tocxref"><span class="secno">2.4.1 </span>External Contexts</a></li></ul></li><li class="tocline"><a href="#from-json-to-json-ld" class="tocxref"><span class="secno">2.5 </span>From JSON to JSON-LD</a></li></ul></li><li class="tocline"><a href="#basic-concepts" class="tocxref"><span class="secno">3. </span>Basic Concepts</a><ul class="toc"><li class="tocline"><a href="#iris" class="tocxref"><span class="secno">3.1 </span>IRIs</a></li><li class="tocline"><a href="#identifying-the-subject" class="tocxref"><span class="secno">3.2 </span>Identifying the Subject</a></li><li class="tocline"><a href="#specifying-the-type" class="tocxref"><span class="secno">3.3 </span>Specifying the Type</a></li><li class="tocline"><a href="#strings" class="tocxref"><span class="secno">3.4 </span>Strings</a></li><li class="tocline"><a href="#string-internationalization" class="tocxref"><span class="secno">3.5 </span>String Internationalization</a></li><li class="tocline"><a href="#typed-literals" class="tocxref"><span class="secno">3.6 </span>Typed Literals</a></li><li class="tocline"><a href="#multiple-objects-for-a-single-property" class="tocxref"><span class="secno">3.7 </span>Multiple Objects for a Single Property</a></li><li class="tocline"><a href="#multiple-typed-literals-for-a-single-property" class="tocxref"><span class="secno">3.8 </span>Multiple Typed Literals for a Single Property</a></li><li class="tocline"><a href="#lists" class="tocxref"><span class="secno">3.9 </span>Lists</a></li></ul></li><li class="tocline"><a href="#advanced-concepts" class="tocxref"><span class="secno">4. </span>Advanced Concepts</a><ul class="toc"><li class="tocline"><a href="#base-uri" class="tocxref"><span class="secno">4.1 </span>Base URI</a></li><li class="tocline"><a href="#default-vocabulary" class="tocxref"><span class="secno">4.2 </span>Default Vocabulary</a></li><li class="tocline"><a href="#default-language" class="tocxref"><span class="secno">4.3 </span>Default Language</a></li><li class="tocline"><a href="#vocabulary-prefixes" class="tocxref"><span class="secno">4.4 </span>Vocabulary Prefixes</a></li><li class="tocline"><a href="#automatic-typing" class="tocxref"><span class="secno">4.5 </span>Automatic Typing</a></li><li class="tocline"><a href="#type-coercion" class="tocxref"><span class="secno">4.6 </span>Type Coercion</a></li><li class="tocline"><a href="#chaining" class="tocxref"><span class="secno">4.7 </span>Chaining</a></li><li class="tocline"><a href="#identifying-unlabeled-nodes" class="tocxref"><span class="secno">4.8 </span>Identifying Unlabeled Nodes</a></li><li class="tocline"><a href="#aliasing-keywords" class="tocxref"><span class="secno">4.9 </span>Aliasing Keywords</a></li></ul></li><li class="tocline"><a href="#using-json-ld-for-rdf" class="tocxref"><span class="secno">5. </span>Using JSON-LD for RDF</a></li><li class="tocline"><a href="#markup-examples" class="tocxref"><span class="secno">A. </span>Markup Examples</a><ul class="toc"><li class="tocline"><a href="#turtle" class="tocxref"><span class="secno">A.1 </span>Turtle</a><ul class="toc"><li class="tocline"><a href="#prefix-and-base-definitions" class="tocxref"><span class="secno">A.1.1 </span>Prefix and Base definitions</a></li><li class="tocline"><a href="#chaining-1" class="tocxref"><span class="secno">A.1.2 </span>Chaining</a></li><li class="tocline"><a href="#lists-1" class="tocxref"><span class="secno">A.1.3 </span>Lists</a></li></ul></li><li class="tocline"><a href="#rdfa" class="tocxref"><span class="secno">A.2 </span>RDFa</a></li><li class="tocline"><a href="#microformats" class="tocxref"><span class="secno">A.3 </span>Microformats</a></li><li class="tocline"><a href="#microdata" class="tocxref"><span class="secno">A.4 </span>Microdata</a></li></ul></li><li class="tocline"><a href="#mashing-up-vocabularies" class="tocxref"><span class="secno">B. </span>Mashing Up Vocabularies</a></li><li class="tocline"><a href="#iana-considerations" class="tocxref"><span class="secno">C. </span>IANA Considerations</a></li><li class="tocline"><a href="#acknowledgements" class="tocxref"><span class="secno">D. </span>Acknowledgements</a></li><li class="tocline"><a href="#references" class="tocxref"><span class="secno">E. </span>References</a><ul class="toc"><li class="tocline"><a href="#normative-references" class="tocxref"><span class="secno">E.1 </span>Normative references</a></li><li class="tocline"><a href="#informative-references" class="tocxref"><span class="secno">E.2 </span>Informative references</a></li></ul></li></ul></div>



  <div id="introduction" class="section">

  <!-- OddPage -->
  <h2><span class="secno">1. </span>Introduction</h2>

  <p>
  JSON, as specified in [<cite><a class="bibref" rel="biblioentry" href="#bib-RFC4627">RFC4627</a></cite>], is a simple language for representing
  data on the Web. <a class="tref internalDFN" title="linked_data" href="#dfn-linked_data">Linked Data</a> is a technique for creating a graph of interlinked data across
  different
  documents or Web sites. Data entities are described using <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>s,
  which are typically dereferencable and thus may be used to find more
  information about an entity, creating a &quot;Web of Knowledge&quot;. JSON-LD is intended to be a simple
  publishing method for expressing not only Linked Data in JSON, but also for adding
  semantics to existing JSON.
  </p>

  <p>
  JSON-LD is designed as a light-weight syntax that can be used to express
  <a class="tref internalDFN" title="linked_data" href="#dfn-linked_data">Linked Data</a>. It is primarily intended to be a way to use Linked Data
  in Javascript and other Web-based programming environments. It is also
  useful when building interoperable Web services and when storing Linked
  Data in JSON-based document storage engines. It is practical and designed
  to be as simple as possible, utilizing the large number of JSON parsers
  and libraries available today. It is designed to be able to
  express key-value pairs, RDF data, RDFa [<cite><a class="bibref" rel="biblioentry" href="#bib-RDFA-CORE">RDFA-CORE</a></cite>] data, Microformats
  [<cite><a class="bibref" rel="biblioentry" href="#bib-MICROFORMATS">MICROFORMATS</a></cite>] data, and Microdata [<cite><a class="bibref" rel="biblioentry" href="#bib-MICRODATA">MICRODATA</a></cite>]. That is, it supports
  every major Web-based structured data model in use today.
  </p>

  <p>
  The syntax does not necessarily require applications to change their JSON, but
  allows to easily add meaning by adding context in a way that is either in-band or
  out-of-band. The syntax is designed to not disturb already deployed systems
  running on JSON, but provide a smooth upgrade path from JSON to JSON with
  added semantics. Finally, the format is intended to be easy to parse, efficient to
  generate, convertible to RDF in one pass, and require a very small memory footprint
  in order to operate.
  </p>

  <div id="how-to-read-this-document" class="section">
  <h3><span class="secno">1.1 </span>How to Read this Document</h3>

  <p>
  This document is a detailed specification for a serialization of Linked
  Data in JSON. The document is primarily intended for the following audiences:
  </p>

  <ul>
    <li>Web developers that want to understand the design decisions and
    language syntax for JSON-LD.</li>
    <li>Software developers that want to encode Microformats, RDFa, or Microdata
    in a way that is cross-language compatible via JSON.</li>
    <li>Software developers that want to implement processors and APIs for
    JSON-LD.</li>
  </ul>

  <p>This specification does not describe the processing algorithms and programming interfaces,
    for those see [<cite><a class="bibref" rel="biblioentry" href="#bib-JSON-LD-API">JSON-LD-API</a></cite>].</p>

  <p>
  To understand the basics in this specification you must first be familiar with
  JSON, which is detailed in [<cite><a class="bibref" rel="biblioentry" href="#bib-RFC4627">RFC4627</a></cite>]. To understand the API and how it is
  intended to operate  in a programming environment, it is useful to have working
  knowledge of the JavaScript programming language [<cite><a class="bibref" rel="biblioentry" href="#bib-ECMA-262">ECMA-262</a></cite>] and
  WebIDL [<cite><a class="bibref" rel="biblioentry" href="#bib-WEBIDL">WEBIDL</a></cite>]. To understand how JSON-LD maps to RDF, it is helpful to be
  familiar with the basic RDF concepts [<cite><a class="bibref" rel="biblioentry" href="#bib-RDF-CONCEPTS">RDF-CONCEPTS</a></cite>].</p>

  <p>
    Examples may contain references to existing vocabularies and use <a class="tref internalDFN" title="prefix" href="#dfn-prefix">prefix</a>es to refer to Web Vocabularies. The following is a list of all vocabularies and their <a class="tref internalDFN" title="prefix" href="#dfn-prefix">prefix</a> abbreviations, as used in this document:
  </p>
  <ul>
    <li>The <a href="http://purl.org/dc/terms/">Dublin Core</a>
    vocabulary (abbreviation: <code>dc</code>, e.g., <code>dc:title</code>)</li>
    <li>The <a href="http://xmlns.com/foaf/0.1/">Friend of a Friend</a>
    vocabulary (abbreviation: <code>foaf</code>, e.g., <code>foaf:knows</code>)</li>
    <li>The <a href="http://www.w3.org/1999/02/22-rdf-syntax-ns#">RDF</a>
    vocabulary (abbreviation: <code>rdf</code>, e.g., <code>rdf:type</code>)</li>
    <li>The <a href="http://www.w3.org/2001/XMLSchema#">XSD</a>
    vocabulary (abbreviation: <code>xsd</code>, e.g., <code>xsd:integer</code>)</li>
  </ul>

  <p>
    JSON [<cite><a class="bibref" rel="biblioentry" href="#bib-RFC4627">RFC4627</a></cite>] defines several terms which are used throughout this document:
    </p><dl>
      <dt><dfn title="json_object" id="dfn-json_object">JSON Object</dfn></dt><dd>
        An object structure is represented as a pair of curly brackets surrounding zero or
        more name/value pairs (or members). A name is a <a class="tref internalDFN" title="string" href="#dfn-string">string</a>. A single colon comes after
        each name, separating the name from the value. A single comma separates a value
        from a following name. The names within an object <em class="rfc2119" title="should">should</em> be unique.
      </dd>
      <dt><dfn title="array" id="dfn-array">array</dfn></dt>
      <dd>
        An array is an ordered collection of values. An array structure is represented as square brackets surrounding zero or more values (or elements). Elements are separated by commas.  Within JSON-LD, array order is not preserved by default, unless
        specific markup is provided (see <a href="#lists">Lists</a>). This is because the basic data model of JSON-LD
        is a <a class="tref internalDFN" title="linked_data_graph" href="#dfn-linked_data_graph">linked data graph</a>, which is inherently unordered.
      </dd>
      <dt><dfn title="string" id="dfn-string">string</dfn></dt><dd>
        A string is a sequence of zero or more Unicode characters, wrapped in double quotes, using backslash escapes. A
        character is represented as a single character string.
      </dd>
      <dt><dfn title="number" id="dfn-number">number</dfn></dt>
      <dd>
        A number is is similar to that used in most programming languages, except that the octal and hexadecimal formats are not used and that leading zeros are not allowed.</dd>
      <dt><dfn title="true" id="dfn-true">true</dfn> and <dfn title="false" id="dfn-false">false</dfn></dt><dd>
        Boolean values.
      </dd>
      <dt><dfn title="null" id="dfn-null">null</dfn></dt><dd>
        The use of the <em>null</em> value is undefined within JSON-LD.
        <div class="issue">Supporting <em>null</em> in JSON-LD might have a number of advantages and should be evaluated. This is currently an <a href="https://github.com/json-ld/json-ld.org/issues/11">open issue</a>.</div>
      </dd>
    </dl>
  <p></p>

  </div>

  <div id="syntax-tokens-and-keywords" class="section">
    <h3><span class="secno">1.2 </span>Syntax Tokens and Keywords</h3>

    <p>JSON-LD specifies a number of syntax tokens and keywords that are using
    in all algorithms described in this section:</p>

    <dl>
    <dt><code>@context</code></dt><dd>Used to set the <a class="tref internalDFN" title="local_context" href="#dfn-local_context">local context</a>.</dd>
    <dt><code>@base</code></dt><dd>Used to set the base <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a> for all object IRIs affected  by the <a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a>.</dd>
    <dt><code>@vocab</code></dt><dd>Used to set the base <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a> for all property IRIs affected by the <a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a>.</dd>
    <dt><code>@coerce</code></dt><dd>Used to specify type coercion rules.</dd>
    <dt><code>@literal</code></dt><dd>Used to specify a literal value.</dd>
    <dt><code>@iri</code></dt><dd>Used to specify an <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a> value.</dd>
    <dt><code>@language</code></dt><dd>Used to specify the language for a literal.</dd>
    <dt><code>@datatype</code></dt><dd>Used to specify the datatype for a literal.</dd>
    <dt><code>:</code></dt><dd>The separator for JSON keys and values that use the <a class="tref internalDFN" title="prefix" href="#dfn-prefix">prefix</a> mechanism.</dd>
    <dt><code>@subject</code></dt><dd>Sets the active subject.</dd>
    <dt><code>@type</code></dt><dd>Used to set the type of the active subject.</dd>
    </dl>
  </div>

  <div id="contributing" class="section">
  <h3><span class="secno">1.3 </span>Contributing</h3>

  <p>There are a number of ways that one may participate in the development of
  this specification:</p>

  <ul>
  <li>Technical discussion typically occurs on the public mailing list:
  <a href="http://lists.w3.org/Archives/Public/public-linked-json/">public-linked-json@w3.org</a>
  </li>

  <li><a href="http://json-ld.org/minutes/">Public teleconferences</a> are held
  on Tuesdays at 1500UTC on the second and fourth week of each month.
  </li>

  <li>Specification bugs and issues should be reported in the
  <a href="https://github.com/json-ld/json-ld.org/issues">issue tracker</a>.</li>

  <li><a href="https://github.com/json-ld/json-ld.org/tree/main/spec">Source code</a> for the
  specification can be found on Github.</li>

  <li>The <a href="http://webchat.freenode.net/?channels=#json-ld">#json-ld</a>
  IRC channel is available for real-time discussion on irc.freenode.net.</li>
  </ul>

  </div>

  </div>

  <div id="design" class="section">

  <!-- OddPage -->
  <h2><span class="secno">2. </span>Design</h2>

  <p>The following section outlines the design goals and rationale behind the
  JSON-LD markup language.
  </p>

  <div id="goals-and-rationale" class="section">
  <h3><span class="secno">2.1 </span>Goals and Rationale</h3>

  <p>
  A number of design considerations were explored during the creation of this
  markup language:
  </p>

  <dl>
   <dt>Simplicity</dt>
   <dd>Developers need only know JSON and three keywords to use the basic
   functionality in JSON-LD. No extra processors or software libraries are
   necessary to use JSON-LD in its most basic form. The language attempts to
   ensure that developers have an easy learning curve.</dd>
   <dt>Compatibility</dt>
   <dd>The JSON-LD markup must be 100% compatible with JSON. This ensures that
   all of the standard JSON libraries work seamlessly with JSON-LD documents.</dd>
   <dt>Expressiveness</dt>
   <dd>The syntax must be able to express directed graphs, which have been proven
   to be able to simply express almost every real world data model.</dd>
   <dt>Terseness</dt>
   <dd>The JSON-LD syntax must be very terse and human readable, requiring as
   little as possible effort from the developer.</dd>

  <!-- <dt>Pragmatism</dt>
   <dd>Mixing the expression of pure Linked Data with data that is not
   linked was an approach that was driven by pragmatism. JSON-LD attempts to be
   more practical than theoretical in its approach to Linked Data.</dd> -->

   <dt>Zero Edits, most of the time</dt>
   <dd>JSON-LD provides a mechanism that allows developers to specify
   <a class="tref internalDFN" title="context" href="#dfn-context">context</a> in a way that is out-of-band. This allows organizations that have
   already deployed large JSON-based infrastructure to add meaning to their
   JSON documents in a way that is not disruptive to their day-to-day operations and is
   transparent to their current customers. At times, mapping JSON to
   a graph representation can become difficult. In these instances, rather than
   having JSON-LD support esoteric markup, we chose not to support the use case
   and support a simplified syntax instead. So, while Zero Edits is a goal,
   it is not always possible without adding great complexity to the language.
   </dd>
   <dt>One-pass Processing</dt>
   <dd>JSON-LD supports one-pass processing, which results in a very small memory 
   footprint when processing documents. For example, to convert a JSON-LD document
   into an RDF document of any kind, only one pass is required over the data.</dd>
  </dl>
  </div>

  <div id="linked-data" class="section">
  <h3><span class="secno">2.2 </span>Linked Data</h3>
  <p>
  The following definition for <a class="tref internalDFN" title="linked_data" href="#dfn-linked_data">Linked Data</a> is the one that will
  be used for this specification.
  </p>
  <ol>
    <li><dfn title="linked_data" id="dfn-linked_data">Linked Data</dfn> is a set of documents, each containing a representation of a linked data graph.</li>
    <li>A <dfn title="linked_data_graph" id="dfn-linked_data_graph">linked data graph</dfn> is an unordered labeled directed graph, where nodes are <a class="tref internalDFN" title="subject" href="#dfn-subject">subject</a>s or <a class="tref internalDFN" title="object" href="#dfn-object">object</a>s, and edges are properties.</li>
    <li>A <dfn title="subject" id="dfn-subject">subject</dfn> is any node in a <a class="tref internalDFN" title="linked_data_graph" href="#dfn-linked_data_graph">linked data graph</a> with at least one outgoing edge.</li>
    <li>A <a class="tref internalDFN" title="subject" href="#dfn-subject">subject</a> <em class="rfc2119" title="should">should</em> be labeled with an <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a> (an Internationalized Resource Identifier as described in [<cite><a class="bibref" rel="biblioentry" href="#bib-RFC3987">RFC3987</a></cite>]).</li>
    <li>An <dfn title="object" id="dfn-object">object</dfn> is a node in a <a class="tref internalDFN" title="linked_data_graph" href="#dfn-linked_data_graph">linked data graph</a> with at least one incoming edge.</li>
    <li>An <a class="tref internalDFN" title="object" href="#dfn-object">object</a> <em class="rfc2119" title="may">may</em> be labeled with an <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>.</li>
    <li>An object <em class="rfc2119" title="may">may</em> be a <a class="tref internalDFN" title="subject" href="#dfn-subject">subject</a> and <a class="tref internalDFN" title="object" href="#dfn-object">object</a> at the same time.</li>
    <li>A <dfn title="property" id="dfn-property">property</dfn> is an edge of the <a class="tref internalDFN" title="linked_data_graph" href="#dfn-linked_data_graph">linked data graph</a>.</li>
    <li>A <a class="tref internalDFN" title="property" href="#dfn-property">property</a> <em class="rfc2119" title="should">should</em> be labeled with an <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>.</li>
    <li>An <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a> that is a label in a <a class="tref internalDFN" title="linked_data_graph" href="#dfn-linked_data_graph">linked data graph</a> <em class="rfc2119" title="should">should</em> be dereferencable to a <a class="tref internalDFN" title="linked_data" href="#dfn-linked_data">Linked Data</a> document describing the labeled <a class="tref internalDFN" title="subject" href="#dfn-subject">subject</a>, <a class="tref internalDFN" title="object" href="#dfn-object">object</a> or <a class="tref internalDFN" title="property" href="#dfn-property">property</a>.</li>
    <li>A <dfn title="literal" id="dfn-literal">literal</dfn> is an <a class="tref internalDFN" title="object" href="#dfn-object">object</a> with a label that is not an <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a></li>
  </ol>

  <p>
  Note that the definition for <a class="tref internalDFN" title="linked_data" href="#dfn-linked_data">Linked Data</a> above is silent on the
  topic of unlabeled nodes. Unlabeled nodes are not considered
  <a class="tref internalDFN" title="linked_data" href="#dfn-linked_data">Linked Data</a>. However, this specification allows for the expression
  of unlabled nodes, as most graph-based data sets on the Web contain a number
  of associated nodes that are not named and thus are not directly
  de-referenceable.
  </p>
  </div>

  <div id="linking-data" class="section">
  <h3><span class="secno">2.3 </span>Linking Data</h3>

  <p>
  An Internationalized Resource Identifier
  (<dfn title="iri" id="dfn-iri"><abbr title="Internationalized Resource Identifier">IRI</abbr></dfn>),
  as described in [<cite><a class="bibref" rel="biblioentry" href="#bib-RFC3987">RFC3987</a></cite>], is a mechanism for representing unique
  identifiers on the web. In <a class="tref internalDFN" title="linked_data" href="#dfn-linked_data">Linked Data</a>, an IRI is commonly
  used for expressing a <a class="tref internalDFN" title="subject" href="#dfn-subject">subject</a>, a <a class="tref internalDFN" title="property" href="#dfn-property">property</a> or an
  <a class="tref internalDFN" title="object" href="#dfn-object">object</a>.
  </p>

  <p>JSON-LD defines a mechanism to map JSON terms, i.e., keys and values, to IRIs. This does not mean
  that JSON-LD requires every key or value to be an IRI, but rather ensures that
  keys and values can be mapped to IRIs if the developer desires to transform
  their data into <a class="tref internalDFN" title="linked_data" href="#dfn-linked_data">Linked Data</a>. There are a few techniques that can ensure
  that developers will generate good Linked Data for the Web. JSON-LD
  formalizes those techniques.
  </p>

  <p>We will be using the following JSON markup as the example for the
  rest of this section:
  </p>

  <pre class="example">{
    &quot;name&quot;: &quot;Manu Sporny&quot;,
    &quot;homepage&quot;: &quot;http://manu.sporny.org/&quot;,
    &quot;avatar&quot;: &quot;http://twitter.com/account/profile_image/manusporny&quot;
  }</pre>
  </div>

  <div id="the-context" class="section">
  <h3><span class="secno">2.4 </span>The Context</h3>

  <p>In JSON-LD, a <dfn title="context" id="dfn-context">context</dfn> is used to map <a class="tref internalDFN" title="term" href="#dfn-term">term</a>s, i.e., keys and values
    in an JSON document, to
    <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>s. A <dfn title="term" id="dfn-term">term</dfn> is a short word that <em class="rfc2119" title="may">may</em> be expanded
  to an <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>. The Web uses IRIs for unambiguous identification. The
  idea is that these <a class="tref internalDFN" title="term" href="#dfn-term">term</a>s mean something that may be of use to
  other developers and that it is useful to give them an unambiguous identifier.
  That is, it is useful for <a class="tref internalDFN" title="term" href="#dfn-term">term</a>s to expand to IRIs so that
  developers don't accidentally step on each other's Web Vocabulary terms.
  For example, the term <code>name</code> may map directly to the IRI
  <code>http://xmlns.com/foaf/0.1/name</code>. This allows JSON-LD documents to
  be constructed using the common JSON practice of simple name/value pairs while
  ensuring that the data is useful outside of the page, API or database in which it
  resides.
  </p>

  <p>These Linked Data <a class="tref internalDFN" title="term" href="#dfn-term">term</a>s are typically collected in a context document that would look something like this:</p>

  <pre class="example">{
    &quot;@context&quot;: {
      &quot;name&quot;: &quot;http://xmlns.com/foaf/0.1/name&quot;,
      &quot;homepage&quot;: &quot;http://xmlns.com/foaf/0.1/homepage&quot;,
      &quot;avatar&quot;: &quot;http://xmlns.com/foaf/0.1/avatar&quot;
    }
  }</pre>

  <p>This context document can then be used in an JSON-LD document by adding a 
  single line. The JSON markup as shown in the previous section could be changed 
  as follows to link to the context document:</p>

  <pre class="example">{
    <span class="diff">&quot;@context&quot;: &quot;http://example.org/json-ld-contexts/person&quot;,</span>
    &quot;name&quot;: &quot;Manu Sporny&quot;,
    &quot;homepage&quot;: &quot;http://manu.sporny.org/&quot;,
    &quot;avatar&quot;: &quot;http://twitter.com/account/profile_image/manusporny&quot;
  }</pre>

  <p>The additions above transform the previous JSON document into a JSON document
  with added semantics because the <code>@context</code> specifies how the
  <strong>name</strong>, <strong>homepage</strong>, and <strong>avatar</strong>
  terms map to IRIs.
  Mapping those keys to IRIs gives the data global context. If two
  developers use the same IRI to describe a property, they are more than likely
  expressing the same concept. This allows both developers to re-use each others
  data without having to agree to how their data will inter-operate on a
  site-by-site basis. Contexts may also contain datatype information
  for certain <a class="tref internalDFN" title="term" href="#dfn-term">term</a>s as well as other processing instructions for
  the JSON-LD processor.</p>

  <p>Contexts may be specified in-line. This ensures that JSON-LD documents
  can be processed when a JSON-LD processor does not have access to the Web.</p>

  <pre class="example">{
    <span class="diff">&quot;@context&quot;: {
      &quot;name&quot;: &quot;http://xmlns.com/foaf/0.1/name&quot;,
      &quot;homepage&quot;: &quot;http://xmlns.com/foaf/0.1/homepage&quot;,
      &quot;avatar&quot;: &quot;http://xmlns.com/foaf/0.1/avatar&quot;
    },</span>
    &quot;name&quot;: &quot;Manu Sporny&quot;,
    &quot;homepage&quot;: &quot;http://manu.sporny.org/&quot;,
    &quot;avatar&quot;: &quot;http://twitter.com/account/profile_image/manusporny&quot;
  }</pre>

  <p>Contexts may be used at any time a <a class="tref internalDFN" title="json_object" href="#dfn-json_object">JSON object</a> is defined, and a <a class="tref internalDFN" title="json_object" href="#dfn-json_object">JSON object</a>
    may specify multiple contexts, to be processed in order, for example to include standard prefix
    definitions along with a local language definition used to set the language of <a class="tref internalDFN" title="plain_literal" href="#dfn-plain_literal">plain literal</a>s:</p>

  <p>
    The set of contexts defined within a specific <a class="tref internalDFN" title="json_object" href="#dfn-json_object">JSON Object</a> is termed a <dfn title="local_context" id="dfn-local_context">local context</dfn>.
    The <dfn title="active_context" id="dfn-active_context">active context</dfn> refers to the accumulation of <a class="tref internalDFN" title="local_context" href="#dfn-local_context">local context</a>s that are in scope
    at a specific point within the document.</p>

  <pre class="example">{
    <span class="diff">&quot;@context&quot;: [
      &quot;http://example.org/json-ld-contexts/person&quot;,
      {
        &quot;@language&quot;: &quot;en&quot;
      }
    ],</span>
    &quot;name&quot;: &quot;Manu Sporny&quot;,
    &quot;homepage&quot;: &quot;http://manu.sporny.org/&quot;,
    &quot;avatar&quot;: &quot;http://twitter.com/account/profile_image/manusporny&quot;
  }</pre>

  <p>JSON-LD strives to ensure that developers don't have to change the JSON
    that is going into and being returned from their Web APIs. This means
    that developers can also specify a <a class="tref internalDFN" title="context" href="#dfn-context">context</a> for JSON data in an out-of-band
    fashion. This is described later in this document. </p>

  <p>
    JSON-LD uses a special type of machine-readable document called a
    <dfn title="web_vocabulary" id="dfn-web_vocabulary">Web Vocabulary</dfn> to define <a class="tref internalDFN" title="term" href="#dfn-term">term</a>s that are then used
    to describe concepts and &quot;things&quot; in the world.
    Typically, these Web Vocabulary documents have <a class="tref internalDFN" title="prefix" href="#dfn-prefix">prefix</a>es associated
    with them and contain a number of <a class="tref internalDFN" title="term" href="#dfn-term">term</a> declarations.
    <a class="tref internalDFN" title="prefix" href="#dfn-prefix">Prefix</a>es are helpful when a developer
    wants to mix multiple vocabularies together in a <a class="tref internalDFN" title="context" href="#dfn-context">context</a>, but does not want
    to go to the trouble of defining every single term in every single vocabulary.
    Some Web Vocabularies may have dozens of terms defined. If a developer wants to use
    3-4 different vocabularies, the number of terms that
    would have to be declared in a single <a class="tref internalDFN" title="context" href="#dfn-context">context</a> could become quite large. To
    reduce the number of different terms that must be defined, JSON-LD also allows
    prefixes to be used to compact IRIs.
  </p><p>

  </p><p>For example, the <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a> <code>http://xmlns.com/foaf/0.1/</code>
  specifies a <a class="tref internalDFN" title="web_vocabulary" href="#dfn-web_vocabulary">Web Vocabulary</a> which may be represented using the
  <code>foaf</code> <a class="tref internalDFN" title="prefix" href="#dfn-prefix">prefix</a>. The <code>foaf</code> Web Vocabulary
  contains a term called <strong>name</strong>. If you join the
  <code>foaf</code> <a class="tref internalDFN" title="prefix" href="#dfn-prefix">prefix</a> with the <strong>name</strong> suffix,
  you can build a compact IRI that will expand out into an absolute IRI for the
  <code>http://xmlns.com/foaf/0.1/name</code> vocabulary term.
  That is, the compact IRI, or short-form, is <code>foaf:name</code> and the
  expanded-form is <code>http://xmlns.com/foaf/0.1/name</code>. This vocabulary
  term is used to specify a person's name.
  </p>

  <p>Developers, and machines, are able to use this <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a> (plugging it
  directly into a web browser, for instance) to go to the term and get a
  definition of what the term means. Much like we can use <a href="http://wordnet.princeton.edu/">WordNet</a> today to
  see the definition
  of words in the English language. Developers and machines need the same sort of
  definition of terms. IRIs provide a way to ensure that these terms
  are unambiguous.
  </p>

  <p>The <a class="tref internalDFN" title="context" href="#dfn-context">context</a> provides a collection of vocabulary <a class="tref internalDFN" title="term" href="#dfn-term">term</a>s and
  <a class="tref internalDFN" title="prefix" href="#dfn-prefix">prefix</a>es that can be used to expand JSON keys and values into
  <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>s.</p>

  <p class="note">To ensure the best possible performance, it is a best practice to
  put the <a class="tref internalDFN" title="context" href="#dfn-context">context</a> definition at the top of the JSON-LD document. If it isn't listed
  first, processors have to save each key-value pair until the <a class="tref internalDFN" title="context" href="#dfn-context">context</a> is processed.
  This creates a memory and complexity burden for one-pass processors.</p>
  <div id="external-contexts" class="section">
    <h4><span class="secno">2.4.1 </span>External Contexts</h4>

    <p>Authors may choose to declare JSON-LD <a class="tref internalDFN" title="context" href="#dfn-context">context</a>s in external 
  documents to promote re-use of contexts as well as reduce the size of JSON-LD 
  documents.
  In order to use an external context, an author <em class="rfc2119" title="may">may</em> specify an <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a> to a valid
  JSON-LD document. The referenced document <em class="rfc2119" title="must">must</em> have a top-level <a class="tref internalDFN" title="json_object" href="#dfn-json_object">JSON Object</a>.
  The value of any <code>@context</code> key within that object is substituted for
  the IRI within the referencing document to have the same effect as if the value were
  specified inline within the referencing document.</p>
    <p>The following example demonstrates the use of an external context:</p>

  <pre class="example">{
    <span class="diff">&quot;@context&quot;: &quot;http://example.org/json-ld-contexts/person&quot;</span>,
    &quot;name&quot;: &quot;Manu Sporny&quot;,
    &quot;homepage&quot;: &quot;http://manu.sporny.org/&quot;,
    &quot;avatar&quot;: &quot;http://twitter.com/account/profile_image/manusporny&quot;
  }</pre>

  <p>Authors may also import multiple contexts or a combination of external and local contexts by specifying a list of 
  contexts:</p>

  <pre class="example">{
    <span class="diff">&quot;@context&quot;: [&quot;http://example.org/json-ld-contexts/person&quot;, &quot;http://example.org/json-ld-contexts/event&quot;]</span>
    &quot;name&quot;: &quot;Manu Sporny&quot;,
    &quot;homepage&quot;: &quot;http://manu.sporny.org/&quot;,
    &quot;avatar&quot;: &quot;http://twitter.com/account/profile_image/manusporny&quot;
    <span class="diff">&quot;celebrates&quot;:
    {
       &quot;@type&quot;: &quot;Event&quot;,
       &quot;description&quot;: &quot;International Talk Like a Pirate Day&quot;,
       &quot;date&quot;: &quot;R/2011-09-19&quot;
    }</span>
  }</pre>

  <p>Each context in a list will be evaluated in-order. Duplicate mappings within the <a class="tref internalDFN" title="context" href="#dfn-context">context</a>s <em class="rfc2119" title="must">must</em> be
  overwritten on a last-defined-overrides basis. The context list <em class="rfc2119" title="must">must</em> contain
  either de-referenceable <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>s or <a class="tref internalDFN" title="json_object" href="#dfn-json_object">JSON Object</a>s that conform to the
  <a class="tref internalDFN" title="context" href="#dfn-context">context</a> syntax as described in this document.</p>

  <p>External JSON-LD context documents <em class="rfc2119" title="may">may</em> contain extra information located
  outside of the <code>@context</code> key, such as
  documentation about the <a class="tref internalDFN" title="prefix" href="#dfn-prefix">prefix</a>es declared in the document. It is
  also <em class="rfc2119" title="recommended">recommended</em> that a human-readable document encoded in HTML+RDFa 
  [<cite><a class="bibref" rel="biblioentry" href="#bib-HTML-RDFA">HTML-RDFA</a></cite>] or other Linked Data compatible format is served as well to
  explain the correct usage of the JSON-LD context document.
  </p>

  </div>

  </div>

  <div id="from-json-to-json-ld" class="section">
  <h3><span class="secno">2.5 </span>From JSON to JSON-LD</h3>

  <p>If a set of terms such as, <strong>name</strong>, <strong>homepage</strong>,
  and <strong>avatar</strong>,
  are defined in a <a class="tref internalDFN" title="context" href="#dfn-context">context</a>, and that context is used to resolve the
  names in JSON objects, machines are able to automatically expand the terms to
  something meaningful and unambiguous, like this:</p>

  <pre class="example">{
    &quot;<span class="diff">http://xmlns.com/foaf/0.1/name</span>&quot;: &quot;Manu Sporny&quot;,
    &quot;<span class="diff">http://xmlns.com/foaf/0.1/homepage</span>&quot;: &quot;http://manu.sporny.org&quot;
    &quot;<span class="diff">http://rdfs.org/sioc/ns#avatar</span>&quot;: &quot;http://twitter.com/account/profile_image/manusporny&quot;
  }</pre>

  <p>Doing this allows JSON to be unambiguously machine-readable without
  requiring developers to drastically change their workflow.</p>
  <p class="note">Please note that this JSON-LD document doesn't define the
  subject and will thus result in an unlabeled or blank node.</p>

  </div>

  </div>



  <div id="basic-concepts" class="section">

  <!-- OddPage -->
  <h2><span class="secno">3. </span>Basic Concepts</h2>

  <p>JSON-LD is designed to ensure that <a class="tref internalDFN" title="linked_data" href="#dfn-linked_data">Linked Data</a> concepts can be marked
  up in a way that is simple to understand and author by Web developers. In many
  cases, regular JSON markup can become Linked Data with the simple addition
  of a <a class="tref internalDFN" title="context" href="#dfn-context">context</a>. As more JSON-LD features are used, more semantics are added
  to the JSON markup.</p>

  <div id="iris" class="section">
  <h3><span class="secno">3.1 </span>IRIs</h3>

  <p>Expressing <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>s are fundamental to <a class="tref internalDFN" title="linked_data" href="#dfn-linked_data">Linked Data</a> as that is how most
  <a class="tref internalDFN" title="subject" href="#dfn-subject">subject</a>s and many <a class="tref internalDFN" title="object" href="#dfn-object">object</a> are named. <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>s can be
  expressed in a variety of different ways in JSON-LD.</p>

  <ol>
    <li>In general, <a class="tref internalDFN" title="term" href="#dfn-term">term</a>s in the key position in
      a <a class="tref internalDFN" title="json_object" href="#dfn-json_object">JSON object</a> that have a mapping to an <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a> or another key in the <a class="tref internalDFN" title="context" href="#dfn-context">context</a> are
      expanded to an IRI by JSON-LD processors. There are special rules for
      processing keys in <code>@context</code> and when dealing with keys that
      start with the <code>@subject</code> character.</li>
    <li>An <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a> is generated for the value specified using <code>@subject</code>,
      if it is a <a class="tref internalDFN" title="string" href="#dfn-string">string</a>.</li>
    <li>An <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a> is generated for the value specified using <code>@type</code>.</li>
    <li>An <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a> is generated for the value specified using the <code>@iri</code>
      keyword.</li>
    <li>An <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a> is generated when there are <code>@coerce</code> rules in
      effect for a key named <code>@iri</code>.</li>
  </ol>

  <p>IRIs can be expressed directly in the key position like so:
  </p>

  <pre class="example">{
  ...
    &quot;<span class="diff">http://xmlns.com/foaf/0.1/name</span>&quot;: &quot;Manu Sporny&quot;,
  ...
  }</pre>

  <p>In the example above, the key
  <code>http://xmlns.com/foaf/0.1/name</code> is interpreted as an <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>, as
  opposed to being interpreted as a string.</p>

  <p>Term expansion occurs for IRIs if a term is defined within the
  <a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a>:</p>

  <pre class="example">{
    &quot;<span class="diff">@context</span>&quot;: {&quot;<span class="diff">name</span>&quot;: &quot;<span class="diff">http://xmlns.com/foaf/0.1/name</span>&quot;},
  ...
    &quot;<span class="diff">name</span>&quot;: &quot;Manu Sporny&quot;,
  ...
  }</pre>

  <p><a class="tref internalDFN" title="prefix" href="#dfn-prefix">Prefix</a>es are expanded when used in keys:</p>

  <pre class="example">{
    &quot;<span class="diff">@context</span>&quot;: {&quot;<span class="diff">foaf</span>&quot;: &quot;<span class="diff">http://xmlns.com/foaf/0.1/</span>&quot;},
  ...
    &quot;<span class="diff">foaf:name</span>&quot;: &quot;Manu Sporny&quot;,
  ...
  }</pre>

  <p><code>foaf:name</code> above will automatically expand out to the IRI
  <code>http://xmlns.com/foaf/0.1/name</code>.</p>

  <p>An <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a> is generated when a value is associated with a key using
  the <code>@iri</code> keyword:</p>

  <pre class="example">{
  ...
    &quot;homepage&quot;: { &quot;<span class="diff">@iri</span>&quot;: &quot;http://manu.sporny.org&quot; }
  ...
  }</pre>

  <p>If type coercion rules are specified in the <code>@context</code> for
  a particular vocabulary term, an IRI is generated:</p>

  <pre class="example">{<span class="diff">
    &quot;@context&quot;:
    {
      ...
      &quot;@coerce&quot;:
      {
        &quot;@iri&quot;: &quot;homepage&quot;
      }
    }</span>
  ...
    &quot;homepage&quot;: &quot;http://manu.sporny.org/&quot;,
  ...
  }</pre>

  <p>Even though the value <code>http://manu.sporny.org/</code> is a <a class="tref internalDFN" title="string" href="#dfn-string">string</a>,
  the type coercion rules will transform the value into an IRI when processed
  by a JSON-LD Processor</p>

  <p>IRIs may be represented as an absolute IRI, a <a class="tref internalDFN" title="term" href="#dfn-term">term</a>, a <a class="tref internalDFN" title="prefix" href="#dfn-prefix">prefix</a>:<a class="tref internalDFN" title="term" href="#dfn-term">term</a> construct, or as a value relative to <code>@base</code> or <code>@vocab</code>.</p>

  </div>

  <div id="identifying-the-subject" class="section">
  <h3><span class="secno">3.2 </span>Identifying the Subject</h3>

  <p>
    To be able to externally reference nodes, it is important that each node has an unambiguous identifier.
    <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>s are a fundamental concept of <a class="tref internalDFN" title="linked_data" href="#dfn-linked_data">Linked Data</a>, and nodes should have a de-referencable
    identifier used to name and locate them. For nodes to be truely linked, de-referencing the identifier
    should result in a representation of that node. Associating an IRI with a node tells an application
    that the returned document contains a description of the node requested.
  </p>
  <p>
    JSON-LD documents may also contain descriptions of other nodes, so it is necessary to be able to
    uniquely identify each node which may be externally referenced.
  </p>
  <p>A <a class="tref internalDFN" title="subject" href="#dfn-subject">subject</a>
     of an object in JSON is declared using the <code>@subject</code> key. The subject is the
  first piece of information needed by the JSON-LD processor in order to
  create the (subject, property, object) tuple, also known as a triple.</p>

  <pre class="example">{
  ...
    &quot;<span class="diff">@subject</span>&quot;: &quot;<span class="diff">http://example.org/people#joebob</span>&quot;,
  ...
  }</pre>

  <p>The example above would set the subject to the IRI
  <code>http://example.org/people#joebob</code>.
  </p>

  <p class="note">To ensure the best possible performance, it is a best practice to
  put the <code>@subject</code> key before other key-value pairs in an object. If
  it isn't listed first, processors have to save each key-value pair until
  <code>@subject</code> is processed before they can create valid triples. This
  creates a memory and complexity burden for one-pass processors.</p>

  </div>

  <div id="specifying-the-type" class="section">
  <h3><span class="secno">3.3 </span>Specifying the Type</h3>

  <p>The type of a particular subject can be specified using the
  <code>@type</code> key. Specifying the type in this way will generate a
  triple of the form (subject, type, type-iri).</p>

  <p>To be <a class="tref internalDFN" title="linked_data" href="#dfn-linked_data">Linked Data</a>, types <em class="rfc2119" title="must">must</em> be uniquely identified by an
    <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>.</p>

  <pre class="example">{
  ...
    &quot;@subject&quot;: &quot;http://example.org/people#joebob&quot;,
    &quot;<span class="diff">@type</span>&quot;: &quot;<span class="diff">http://xmlns.com/foaf/0.1/Person</span>&quot;,
  ...
  }</pre>

  <p>The example above would generate the following triple if the JSON-LD
  document is mapped to RDF (in N-Triples notation):</p>

  <pre class="example">&lt;http://example.org/people#joebob&gt;
     &lt;http://www.w3.org/1999/02/22-rdf-syntax-ns#type&gt;
        &lt;http://xmlns.com/foaf/0.1/Person&gt; .</pre>

  </div>

  <div id="strings" class="section">
  <h3><span class="secno">3.4 </span>Strings</h3>

  <p>Regular text strings, also referred to as <dfn title="plain_literal" id="dfn-plain_literal">plain literal</dfn>s, are
  easily expressed using regular JSON <a class="tref internalDFN" title="string" href="#dfn-string">string</a>s.</p>

  <pre class="example">{
  ...
    &quot;name&quot;: &quot;<span class="diff">Mark Birbeck</span>&quot;,
  ...
  }</pre>

  </div>

  <div id="string-internationalization" class="section">
  <h3><span class="secno">3.5 </span>String Internationalization</h3>

  <p>JSON-LD makes an assumption that strings with associated language encoding
  information are not very common when used in JavaScript and Web Services.
  Thus, it takes a little more effort to express strings with associated
  language information.</p>

  <pre class="example">{
  ...
    &quot;name&quot;: <span class="diff">
    {
      &quot;@literal&quot;: &quot;花澄&quot;,
      &quot;@language&quot;: &quot;ja&quot;
    }</span>
  ...
  }</pre>

  <p>The example above would generate a <a class="tref internalDFN" title="plain_literal" href="#dfn-plain_literal">plain literal</a> for
  <em>花澄</em> and associate the <code>ja</code> language code with the triple
  that is generated. Languages <em class="rfc2119" title="must">must</em> be expressed in [<cite><a class="bibref" rel="biblioentry" href="#bib-BCP47">BCP47</a></cite>] format.</p>

  <p>It is also possible to set a language to use within a <code>@context</code>, to allow specify a language
  to apply to all <a class="tref internalDFN" title="plain_literal" href="#dfn-plain_literal">plain literal</a>s within the scope of the <a class="tref internalDFN" title="context" href="#dfn-context">context</a></p>

  <pre class="example">{
    <span class="diff">&quot;@context:&quot; {
      &quot;@language&quot;: &quot;ja&quot;
    },</span>
  ...
    &quot;name&quot;: <span class="diff">&quot;花澄&quot;</span>
  ...
  }</pre>
  </div>

  <div id="typed-literals" class="section">
  <h3><span class="secno">3.6 </span>Typed Literals</h3>

  <p>
    A value with an associated datatype, also known as a
    <dfn title="typed_literal" id="dfn-typed_literal">typed literal</dfn>, is indicated by associating a literal with
    an <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a> which indicates the literal's datatype. Typed literals may be
    expressed in JSON-LD in three ways:
  </p>

  <ol>
    <li>By utilizing the <code>@coerce</code> keyword.</li>
    <li>By utilizing the expanded form for specifying objects.</li>
    <li>By using a native JSON datatype.</li>
  </ol>

  <p>The first example uses the <code>@coerce</code> keyword to express a
  typed literal:</p>

  <pre class="example">{<span class="diff">
    &quot;@context&quot;:
    {
      &quot;modified&quot;:  &quot;http://purl.org/dc/terms/modified&quot;,
      &quot;dateTime&quot;: &quot;http://www.w3.org/2001/XMLSchema#dateTime&quot;
      &quot;@coerce&quot;:
      {
        &quot;dateTime&quot;: &quot;modified&quot;
      }
    }</span>
  ...
    &quot;modified&quot;: &quot;2010-05-29T14:17:39+02:00&quot;,
  ...
  }</pre>

  <p>The second example uses the expanded form for specifying objects:</p>

  <pre class="example">{
  ...
    &quot;modified&quot;: <span class="diff">
    {
      &quot;@literal&quot;: &quot;2010-05-29T14:17:39+02:00&quot;,
      &quot;@datatype&quot;: &quot;dateTime&quot;
    }</span>
  ...
  }</pre>

  <p>Both examples above would generate an object with the literal value of
  <code>2010-05-29T14:17:39+02:00</code> and the datatype of
  <code>http://www.w3.org/2001/XMLSchema#dateTime</code>.</p>

  <p>The third example uses a built-in native JSON type, a
    <a class="tref internalDFN" title="number" href="#dfn-number">number</a>, to express a datatype:</p>

  <pre class="example">{
  ...
    &quot;@subject&quot;: &quot;http://example.org/people#joebob&quot;,
    &quot;age&quot;: <span class="diff">31</span>
  ...
  }</pre>

  <p>The example above would generate the following triple:</p>

  <pre class="example">&lt;http://example.org/people#joebob&gt;
     &lt;http://xmlns.com/foaf/0.1/age&gt;
        &quot;31&quot;^^&lt;http://www.w3.org/2001/XMLSchema#integer&gt; .</pre>

  </div>

  <div id="multiple-objects-for-a-single-property" class="section">
  <h3><span class="secno">3.7 </span>Multiple Objects for a Single Property</h3>

  <p>A JSON-LD author can express multiple triples in a compact way by using
  <a class="tref internalDFN" title="array" href="#dfn-array">array</a>s. If a subject has multiple values for the same property, the author
  <em class="rfc2119" title="may">may</em> express each property as an <a class="tref internalDFN" title="array" href="#dfn-array">array</a>.</p>

  <p class="note">In JSON-LD, multiple objects on a property are not ordered. This is because typically graphs
  are not inherently ordered data structures. To see more on creating ordered collections
  in JSON-LD, see <a href="#lists">Lists</a>.
  </p>

  <pre class="example">{
  ...
    &quot;@subject&quot;: &quot;http://example.org/people#joebob&quot;,
    &quot;nick&quot;: <span class="diff">[&quot;joe&quot;, &quot;bob&quot;, &quot;jaybee&quot;]</span>,
  ...
  }</pre>

  <p>The markup shown above would generate the following triples:</p>

  <pre class="example">&lt;http://example.org/people#joebob&gt;
     &lt;http://xmlns.com/foaf/0.1/nick&gt;
        &quot;joe&quot; .
  &lt;http://example.org/people#joebob&gt;
     &lt;http://xmlns.com/foaf/0.1/nick&gt;
        &quot;bob&quot; .
  &lt;http://example.org/people#joebob&gt;
     &lt;http://xmlns.com/foaf/0.1/nick&gt;
        &quot;jaybee&quot; .</pre>

  </div>

  <div id="multiple-typed-literals-for-a-single-property" class="section">
  <h3><span class="secno">3.8 </span>Multiple Typed Literals for a Single Property</h3>

  <p>Multiple <a class="tref internalDFN" title="typed_literal" href="#dfn-typed_literal">typed literal</a>s may also be expressed using the expanded
  form for objects:</p>

  <pre class="example">{
  ...
    &quot;@subject&quot;: &quot;http://example.org/articles/8&quot;,
    &quot;modified&quot;: <span class="diff">
    [
      {
        &quot;@literal&quot;: &quot;2010-05-29T14:17:39+02:00&quot;,
        &quot;@datatype&quot;: &quot;dateTime&quot;
      },
      {
        &quot;@literal&quot;: &quot;2010-05-30T09:21:28-04:00&quot;,
        &quot;@datatype&quot;: &quot;dateTime&quot;
      }
    ]</span>
  ...
  }</pre>

  <p>The markup shown above would generate the following triples:</p>

  <pre class="example">&lt;http://example.org/articles/8&gt;
     &lt;http://purl.org/dc/terms/modified&gt;
        &quot;2010-05-29T14:17:39+02:00&quot;^^http://www.w3.org/2001/XMLSchema#dateTime .
  &lt;http://example.org/articles/8&gt;
     &lt;http://purl.org/dc/terms/modified&gt;
        &quot;2010-05-30T09:21:28-04:00&quot;^^http://www.w3.org/2001/XMLSchema#dateTime .</pre>

  </div>

  <div id="lists" class="section">
    <h3><span class="secno">3.9 </span>Lists</h3>
    <p>
      Because graphs do not describe ordering for links between nodes,  in contrast to plain JSON, multi-valued properties
      in JSON-LD do not provide an ordering of the listed objects. For example, consider the following
      simple document:
    </p>
    <pre class="example">{
  ...
    &quot;@subject&quot;: &quot;http://example.org/people#joebob&quot;,
    &quot;nick&quot;: <span class="diff">[&quot;joe&quot;, &quot;bob&quot;, &quot;jaybee&quot;]</span>,
  ...
  }</pre>
    <p>
      This results in three triples being generated, each relating the subject to an individual
      object, with no inherent order.</p>
    <p>To preserve the order of the objects, RDF-based languages, such as [<cite><a class="bibref" rel="biblioentry" href="#bib-TURTLE">TURTLE</a></cite>]
      use the concept of an <code>rdf:List</code> (as described in [<cite><a class="bibref" rel="biblioentry" href="#bib-RDF-SCHEMA">RDF-SCHEMA</a></cite>]). This uses a sequence
      of unlabeled nodes with properties describing a value, a null-terminated next property. Without
      specific syntactical support, this could be represented in JSON-LD as follows:
    </p>
    <pre class="example">{
  ...
    &quot;@subject&quot;: &quot;http://example.org/people#joebob&quot;,
    &quot;nick&quot;: <span class="diff">{</span>,
      <span class="diff">&quot;@first&quot;: &quot;joe&quot;</span>,
      <span class="diff">&quot;@rest&quot;: {</span>
        <span class="diff">&quot;@first&quot;: &quot;bob&quot;</span>,
        <span class="diff">&quot;@rest&quot;: {</span>
          <span class="diff">&quot;@first&quot;: &quot;jaybee&quot;</span>,
          <span class="diff">&quot;@rest&quot;: &quot;@nil&quot;</span>
          <span class="diff">}</span>
        <span class="diff">}</span>
      <span class="diff">}</span>
    <span class="diff">}</span>,
  ...
  }</pre>
    <p>
      As this notation is rather unwieldy and the notion of ordered collections is rather important
      in data modeling, it is useful to have specific language support. In JSON-LD, a list may
      be represented using the <code>@list</code> keyword as follows:
    </p>
    <pre class="example">{
  ...
    &quot;@subject&quot;: &quot;http://example.org/people#joebob&quot;,
    &quot;foaf:nick&quot;: <span class="diff">{&quot;@list&quot;: [&quot;joe&quot;, &quot;bob&quot;, &quot;jaybee&quot;]}</span>,
  ...
  }</pre>
    <p>
      This describes the use of this <a class="tref internalDFN" title="array" href="#dfn-array">array</a> as being ordered, and order is maintained through normalization
      and RDF conversion as described in [<cite><a class="bibref" rel="biblioentry" href="#bib-JSON-LD-API">JSON-LD-API</a></cite>]. If every use of a given multi-valued property is a list, this
      may be abbreviated by adding an <code>@coerce</code> term:
    </p>
    <pre class="example">{
    <span class="diff">&quot;@context&quot;: {</span>
      ...
      <span class="diff">&quot;@coerce&quot;: {</span>
        <span class="diff">&quot;@list&quot;: [&quot;foaf:nick&quot;]</span>
      <span class="diff">}</span>
    <span class="diff">}</span>,
  ...
    &quot;@subject&quot;: &quot;http://example.org/people#joebob&quot;,
    &quot;foaf:nick&quot;: <span class="diff">[&quot;joe&quot;, &quot;bob&quot;, &quot;jaybee&quot;]</span>,
  ...
  }</pre>
    <p>
      The @list keyword can be used within the <code>@coerce</code> section of a <code>@context</code> to
      cause value arrays to be coerced into an ordered list.
    </p>
  </div>

  </div>

  <div id="advanced-concepts" class="section">

  <!-- OddPage -->
  <h2><span class="secno">4. </span>Advanced Concepts</h2>

  <p>JSON-LD has a number of features that provide functionality above and beyond
  the core functionality described above. The following sections outline the
  features that are specific to JSON-LD.
  </p>


  <div id="base-uri" class="section">
  <h3><span class="secno">4.1 </span>Base URI</h3>
  <p>JSON-LD allows <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>s to be specified in a relative form. For <a class="tref internalDFN" title="subject" href="#dfn-subject">subject</a> and <a class="tref internalDFN" title="object" href="#dfn-object">object</a>
    IRIs, relative IRIs are resolved against the document base using
    <cite><a href="http://www.ietf.org/rfc/rfc2396.txt">section 5.1 Establishing a
    Base URI</a></cite> of [<cite><a class="bibref" rel="biblioentry" href="#bib-RFC3986">RFC3986</a></cite>]. This value may be explicitly
    set with a <a class="tref internalDFN" title="context" href="#dfn-context">context</a> using the <code>@base</code> keyword.</p>

  <p>For example, if a JSON-LD document was retrieved from <code>http://manu.sporny.org/</code>,
    relative IRIs would resolve against that URI:</p>

  <pre class="example">{
    <span class="diff">&quot;@subject&quot;: &quot;about/&quot;</span>,
    &quot;http://xmlns.com/foaf/0.1/name&quot;: &quot;Manu Sporny&quot;,
    &quot;http://xmlns.com/foaf/0.1/homepage: &quot;&quot;
  }</pre>

  <p>This document uses an empty <code>@subject</code>, which resolves to the document base. However, if
    the document is moved to a different location, the subject IRI would change. To prevent this, a <a class="tref internalDFN" title="context" href="#dfn-context">context</a>
    may have a <code>@base</code> mapping, to set an absolute base for the document in spite of where
    it actually is retrieved from. It <em class="rfc2119" title="must">must</em> have a value of a simple
    <a class="tref internalDFN" title="string" href="#dfn-string">string</a> with the lexical form of an absolute <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>.</p>

  <pre class="example">{
    <span class="diff">&quot;@context&quot;: { &quot;@base&quot;: &quot;http://manu.sporny.org/&quot;}</span>,
    &quot;@subject&quot;: &quot;about/&quot;,
    &quot;http://xmlns.com/foaf/0.1/name&quot;: &quot;Manu Sporny&quot;,
    &quot;http://xmlns.com/foaf/0.1/homepage: &quot;&quot;
  }</pre>
  </div>

  <div id="default-vocabulary" class="section">
  <h3><span class="secno">4.2 </span>Default Vocabulary</h3>
  <p>It is often common that all types and properties come from the same vocabulary. JSON-LD provides
    a way to set a base URI to be used for all properties and types that aren't based on terms,
    prefixes or absolute IRIs. Much like the <code>@base</code> keyword, the <code>@vocab</code> keyword
    can be used to set a base <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a> to use for all types and properties that don't otherwise resolve to
    an absolute <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>.

  </p><pre class="example">{
    <span class="diff">&quot;@context&quot;: { &quot;@vocab&quot;: &quot;http://xmlns.com/foaf/1.0/&quot; },</span>
    <span class="diff">&quot;@type&quot;: &quot;Person&quot;</span>,
    &quot;name&quot;: &quot;Manu Sporny&quot;,
    &quot;homepage&quot;: &quot;http://manu.sporny.org/&quot;,
    &quot;avatar&quot;: &quot;http://twitter.com/account/profile_image/manusporny&quot;
  }</pre>
  </div>

  <div id="default-language" class="section">
  <h3><span class="secno">4.3 </span>Default Language</h3>
  <p>JSON-LD allows a default value to use as the language for <a class="tref internalDFN" title="plain_literal" href="#dfn-plain_literal">plain literal</a>s.
    It is commonly the case that documents are written using a single language. As described in
    <a href="string-internationalization">String Internationalization</a>, a language-tagged literal
    may be specified as follows:</p>

  <pre class="example">{
  ...
    &quot;name&quot;:
    {
      &quot;@literal&quot;: &quot;花澄&quot;,
      &quot;@language&quot;: &quot;ja&quot;
    }
  ...
  }</pre>

  <p>By specifying <code>@language</code> within a <a class="tref internalDFN" title="context" href="#dfn-context">context</a>, multiple language-tagged literals may be
    marked up using a simple string form:</p>
  </div>

  <pre class="example">{
    <span class="diff">&quot;@context&quot;: { &quot;@language&quot;: &quot;ja&quot;}</span>,
  ...
    &quot;name&quot;: <span class="diff">&quot;花澄&quot;</span>
  ...
  }</pre>
  <div id="vocabulary-prefixes" class="section">
    <h3><span class="secno">4.4 </span>Vocabulary Prefixes</h3>
    <p>
      Vocabulary terms in <a class="tref internalDFN" title="linked_data" href="#dfn-linked_data">Linked Data</a> documents may draw from a number of
      different Web vocabularies. At times, declaring every single term that
      a document uses can require the developer to declare tens, if not
      hundreds of potential vocabulary terms that may be used across an
      application. This is a concern for at least three reasons; the
      first is the cognitive load on the developer, the second is
      the serialized size of the <a class="tref internalDFN" title="context" href="#dfn-context">context</a>, the third is future-proofing
      application contexts. In order to address these issues, the concept of a
      <a class="tref internalDFN" title="prefix" href="#dfn-prefix">prefix</a> mechanism is introduced.</p>
    <p>
      A <dfn title="prefix" id="dfn-prefix">prefix</dfn> is a compact way of expressing a base
      <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a> to a <a class="tref internalDFN" title="web_vocabulary" href="#dfn-web_vocabulary">Web Vocabulary</a>.
      Generally, these prefixes are used by concatenating the <em>prefix</em> and
      a <em>suffix</em> separated by a colon (<code>:</code>).
      The <a class="tref internalDFN" title="prefix" href="#dfn-prefix">prefix</a> is a <a class="tref internalDFN" title="term" href="#dfn-term">term</a> taken from the <a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a>,
      a short string that identifies a particular Web vocabulary.
      For example, the prefix <code>foaf</code> may be used as a short
      hand for the Friend-of-a-Friend Web Vocabulary, which is identified using
      the IRI <code>http://xmlns.com/foaf/0.1/</code>. A developer may append any of
      the FOAF Vocabulary terms to the end of the prefix to specify a short-hand
      version of the absolute IRI for the vocabulary term. For example,
      <code>foaf:name</code> would be expanded out to the IRI
      <code>http://xmlns.com/foaf/0.1/name</code>. Instead of having to remember
      and type out the entire IRI, the developer can instead use the prefix in
      their JSON-LD markup.
    </p>
    <p>
      The ability to use <a class="tref internalDFN" title="prefix" href="#dfn-prefix">prefix</a>es reduces the need for developers
      to declare every vocabulary term that they intend to use in
      the JSON-LD <a class="tref internalDFN" title="context" href="#dfn-context">context</a>. This reduces document serialization size because
      every vocabulary term need not be declared in the context.
      <a class="tref internalDFN" title="prefix" href="#dfn-prefix">Prefix</a> also
      reduce the cognitive load on the developer. It is far easier to
      remember <code>foaf:name</code> than it is to remember
      <code>http://xmlns.com/foaf/0.1/name</code>. The use of prefixes also
      ensures that a <a class="tref internalDFN" title="context" href="#dfn-context">context</a> document does not have to be updated in lock-step
      with an externally defined <a class="tref internalDFN" title="web_vocabulary" href="#dfn-web_vocabulary">Web Vocabulary</a>. Without prefixes, a developer
      would need to keep their application context terms in lock-step with an
      externally defined Web Vocabulary. Rather, by just declaring the
      Web Vocabulary prefix, one can use new terms as they're declared
      without having to update the application's JSON-LD <a class="tref internalDFN" title="context" href="#dfn-context">context</a>.
    </p>
    <p>Consider the following example:</p>
    <pre class="example">{
    &quot;@context&quot;: {
      <span class="diff">&quot;dc&quot;: &quot;http://purl.org/dc/elements/1.1/&quot;,</span>
      <span class="diff">&quot;ex&quot;: &quot;http://example.org/vocab#&quot;</span>
    },
    &quot;@subject&quot;: &quot;http://example.org/library&quot;,
    &quot;@type&quot;: <span class="diff">&quot;ex:Library&quot;</span>,
    <span class="diff">&quot;ex:contains&quot;</span>: {
      &quot;@subject&quot;: &quot;http://example.org/library/the-republic&quot;,
      &quot;@type&quot;: <span class="diff">&quot;ex:Book&quot;</span>,
      <span class="diff">&quot;dc:creator&quot;</span>: &quot;Plato&quot;,
      <span class="diff">&quot;dc:title&quot;</span>: &quot;The Republic&quot;,
      <span class="diff">&quot;ex:contains&quot;</span>: {
        &quot;@subject&quot;: &quot;http://example.org/library/the-republic#introduction&quot;,
        &quot;@type&quot;: <span class="diff">&quot;ex:Chapter&quot;</span>,
        <span class="diff">&quot;dc:description&quot;</span>: &quot;An introductory chapter on The Republic.&quot;,
        <span class="diff">&quot;dc:title&quot;</span>: &quot;The Introduction&quot;
      },
    },
  }</pre>
    <p>
      In this example, two different vocabularies are referred to using
      prefixes. Those prefixes are then used as type and property values using
      the <code>prefix:suffix</code> notation.
    </p>
    <p>
      Prefixes, also known as CURIEs, are defined more formally in RDFa Core 1.1,
      <cite><a href="http://www.w3.org/TR/rdfa-core/#s_curies">Section 6
      &quot;CURIE Syntax Definition&quot;</a></cite> [<cite><a class="bibref" rel="biblioentry" href="#bib-RDFA-CORE">RDFA-CORE</a></cite>].
      JSON-LD does not support the square-bracketed CURIE syntax as the
      mechanism is not required to disambiguate <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>s in a JSON-LD document like
      it is in HTML documents.
    </p>
  </div>

  <div id="automatic-typing" class="section">
  <h3><span class="secno">4.5 </span>Automatic Typing</h3>

  <p>Since JSON is capable of expressing typed information such as doubles,
  integers, and boolean values. As demonstrated below, JSON-LD utilizes that
  information to create <a class="tref internalDFN" title="typed_literal" href="#dfn-typed_literal">typed literal</a>s:</p>

  <pre class="example">{
  ...
    // The following two values are automatically converted to a type of xsd:double
    // and both values are equivalent to each other.
    &quot;measure:cups&quot;: <span class="diff">5.3</span>,
    &quot;measure:cups&quot;: <span class="diff">5.3e0</span>,
    // The following value is automatically converted to a type of xsd:double as well
    &quot;space:astronomicUnits&quot;: <span class="diff">6.5e73</span>,
    // The following value should never be converted to a language-native type
    &quot;measure:stones&quot;: <span class="diff">{ &quot;@literal&quot;: &quot;4.8&quot;, &quot;@datatype&quot;: &quot;xsd:decimal&quot; }</span>,
    // This value is automatically converted to having a type of xsd:integer
    &quot;chem:protons&quot;: <span class="diff">12</span>,
    // This value is automatically converted to having a type of xsd:boolean
    &quot;sensor:active&quot;: <span class="diff">true</span>,
  ...
  }</pre>

  <p class="note">When dealing with a number of modern programming languages,
  including JavaScript ECMA-262, there is no distinction between
  <strong>xsd:decimal</strong> and <strong>xsd:double</strong> values. That is,
  the <a class="tref internalDFN" title="number" href="#dfn-number">number</a> <code>5.3</code> and the <a class="tref internalDFN" title="number" href="#dfn-number">number</a>
  <code>5.3e0</code> are treated as if they were the same. When converting from
  JSON-LD to a language-native format and back, datatype information is lost in a
  number of these languages. Thus, one could say that <code>5.3</code> is a
  <strong>xsd:decimal</strong> and <code>5.3e0</code> is an
  <strong>xsd:double</strong> in JSON-LD, but when both values are
  converted to a language-native format the datatype difference between the two
  is lost because the machine-level representation will almost always be a
  <strong>double</strong>.
  Implementers should be aware of this potential round-tripping issue between
  <strong>xsd:decimal</strong> and <strong>xsd:double</strong>. Specifically
  objects with a datatype of <strong>xsd:decimal</strong> <em class="rfc2119" title="must not">must not</em> be converted
  to a language native type.
  </p>

  </div>

  <div id="type-coercion" class="section">
  <h3><span class="secno">4.6 </span>Type Coercion</h3>

  <p>JSON-LD supports the coercion of values to particular data types.
  Type coercion allows someone deploying JSON-LD to coerce the incoming or
  outgoing types to the proper data type based on a mapping of data type <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>s to
  property types. Using type coercion, one may convert simple JSON data to
  properly typed RDF data.</p>

  <p>The example below demonstrates how a JSON-LD author can coerce values to
  <a class="tref internalDFN" title="plain_literal" href="#dfn-plain_literal">plain literal</a>s, <a class="tref internalDFN" title="typed_literal" href="#dfn-typed_literal">typed literal</a>s and IRIs.</p>

  <pre class="example">{
    &quot;@context&quot;:
    {
       &quot;rdf&quot;: &quot;http://www.w3.org/1999/02/22-rdf-syntax-ns#&quot;,
       &quot;xsd&quot;: &quot;http://www.w3.org/2001/XMLSchema#&quot;,
       &quot;name&quot;: &quot;http://xmlns.com/foaf/0.1/name&quot;,
       &quot;age&quot;: &quot;http://xmlns.com/foaf/0.1/age&quot;,
       &quot;homepage&quot;: &quot;http://xmlns.com/foaf/0.1/homepage&quot;,
  <span class="diff">     &quot;@coerce&quot;:
       {
          &quot;xsd:integer&quot;: &quot;age&quot;,
          &quot;@iri&quot;: &quot;homepage&quot;
       }</span>
    },
    &quot;name&quot;: &quot;John Smith&quot;,
    &quot;age&quot;: <span class="diff">&quot;41&quot;</span>,
    &quot;homepage&quot;: <span class="diff">&quot;http://example.org/home/&quot;</span>
  }</pre>

  <p>The example above would generate the following triples:</p>

  <pre class="example">_:bnode1
     &lt;http://xmlns.com/foaf/0.1/name&gt;
        &quot;John Smith&quot; .
  _:bnode1
     &lt;http://xmlns.com/foaf/0.1/age&gt;
        &quot;41&quot;^^http://www.w3.org/2001/XMLSchema#integer .
  _:bnode1
     &lt;http://xmlns.com/foaf/0.1/homepage&gt;
        &lt;http://example.org/home/&gt; .</pre>

  <div class="issue">
    <p>The mechanism for type coercion is still being debated. It may be that the key/value
      positions are swapped, yielding a <code>@context</code> such as the following:</p>

  <pre class="example">{
    &quot;@context&quot;: {
      &quot;rdf&quot;: &quot;http://www.w3.org/1999/02/22-rdf-syntax-ns#&quot;,
      &quot;xsd&quot;: &quot;http://www.w3.org/2001/XMLSchema#&quot;,
      &quot;name&quot;: &quot;http://xmlns.com/foaf/0.1/name&quot;,
      &quot;age&quot;: &quot;http://xmlns.com/foaf/0.1/age&quot;,
      &quot;homepage&quot;: &quot;http://xmlns.com/foaf/0.1/homepage&quot;,
      &quot;currentProject&quot;: &quot;http://xmlns.com/foaf/0.1/currentProject&quot;,
      <span class="diff">&quot;@coerce&quot;: {
        &quot;age&quot;: &quot;xsd:integer&quot;,
        &quot;homepage&quot;: &quot;@iri&quot;,
        &quot;currentProject&quot;: [&quot;@iri&quot;, &quot;@list&quot;]
       }</span>
    },
    ...
  }</pre>

  <p>An alternative is to merge the coercion into term definitions:</p>

  <pre class="example">{
    &quot;@context&quot;:
    {
      &quot;rdf&quot;: &quot;http://www.w3.org/1999/02/22-rdf-syntax-ns#&quot;,
      &quot;xsd&quot;: &quot;http://www.w3.org/2001/XMLSchema#&quot;,
      &quot;name&quot;: &quot;http://xmlns.com/foaf/0.1/name&quot;,
      &quot;age&quot;: <span class="diff">{&quot;@iri&quot;: &quot;http://xmlns.com/foaf/0.1/age&quot;, &quot;@coerce&quot;: &quot;xsd:integer&quot;}</span>,
      &quot;homepage&quot;: <span class="diff">{&quot;@iri&quot;: &quot;http://xmlns.com/foaf/0.1/age&quot;, &quot;@coerce&quot;: &quot;@iri&quot;}</span>,
      &quot;currentProject&quot;: <span class="diff">{&quot;@iri&quot;: &quot;http://xmlns.com/foaf/0.1/currentProject&quot;, &quot;@coerce&quot;: [&quot;@iri&quot;, &quot;@list&quot;]}</span>,
    },
    ...
  }</pre>
  </div>

  </div>

  <div id="chaining" class="section">
    <h3><span class="secno">4.7 </span>Chaining</h3>
    <p>
      Object <dfn title="chaining" id="dfn-chaining">chaining</dfn> is a JSON-LD feature that allows an author to
      use the definition of JSON-LD objects as <a class="tref internalDFN" title="property" href="#dfn-property">property</a> values. This
      is a commonly used mechanism for creating a parent-child relationship
      between two <a class="tref internalDFN" title="subject" href="#dfn-subject">subject</a>s.
    </p>
    <p>The example shows an two subjects related by a property from the first
    subject:</p>

    <pre class="example">{
  ...
    &quot;name&quot;: &quot;Manu Sporny&quot;,
    &quot;<span class="diff">knows</span>&quot;: {
      &quot;<span class="diff">@type</span>&quot;: &quot;<span class="diff">Person</span>&quot;,
      &quot;<span class="diff">name</span>&quot;: &quot;<span class="diff">Gregg Kellogg</span>&quot;,
    }
  ...
  }</pre>

    <p>
      An object definition, like the one used above, <em class="rfc2119" title="may">may</em> be used as a
      JSON value at any point in JSON-LD.
    </p>
  </div>

  <div id="identifying-unlabeled-nodes" class="section">
  <h3><span class="secno">4.8 </span>Identifying Unlabeled Nodes</h3>

  <p>At times, it becomes necessary to be able to express information without
  being able to specify the subject. Typically, this type of node is called
  an unlabeled node or a blank node. In JSON-LD, unlabeled node identifiers are
  automatically created if a subject is not specified using the
  <code>@subject</code> keyword. However, authors may provide identifiers for
  unlabeled nodes by using the special <code>_</code> (underscore)
  <a class="tref internalDFN" title="prefix" href="#dfn-prefix">prefix</a>. This allows to reference the node locally within the
  document but not in an external document.</p>

  <pre class="example">{
  ...
    &quot;@subject&quot;: &quot;<span class="diff">_:foo</span>&quot;,
  ...
  }</pre>

  <p>The example above would set the subject to <code>_:foo</code>, which can
  then be used later on in the JSON-LD markup to refer back to the
  unlabeled node. This practice, however, is usually frowned upon when
  generating <a class="tref internalDFN" title="linked_data" href="#dfn-linked_data">Linked Data</a>. If a developer finds that they refer to the unlabeled
  node more than once, they should consider naming the node using a resolve-able
  <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>.
  </p>

  </div>

  <div id="aliasing-keywords" class="section">
  <h3><span class="secno">4.9 </span>Aliasing Keywords</h3>

  <p>JSON-LD allows all of the syntax keywords, except for <code>@context</code>,
  to be aliased. This feature allows more legacy JSON content to be supported
  by JSON-LD. It also allows developers to design domain-specific implementations
  using only the JSON-LD <a class="tref internalDFN" title="context" href="#dfn-context">context</a>.</p>

  <pre class="example">{
    &quot;@context&quot;:
    {
       <span class="diff">&quot;url&quot;: &quot;@subject&quot;</span>,
       <span class="diff">&quot;a&quot;: &quot;@type&quot;</span>,
       &quot;name&quot;: &quot;http://schema.org/name&quot;
    },
    &quot;url&quot;: &quot;http://example.com/about#gregg&quot;,
    &quot;a&quot;: &quot;http://schema.org/Person&quot;,
    &quot;name&quot;: &quot;Gregg Kellogg&quot;
  }</pre>

  <p>In the example above, the <code>@subject</code> and <code>@type</code>
  keywords have been given the aliases <strong>url</strong> and
  <strong>a</strong>, respectively.
  </p>

  </div>

  </div>

  <div id="using-json-ld-for-rdf" class="section">

  <!-- OddPage -->
  <h2><span class="secno">5. </span>Using JSON-LD for RDF</h2>

    <p>JSON-LD is a specification for representing <a class="tref internalDFN" title="linked_data" href="#dfn-linked_data">Linked Data</a> in JSON. A common
      way of working with Linked Data is through <dfn title="rdf" id="dfn-rdf">RDF</dfn>, the Resource Description Framework.
      RDF can be expressed using JSON-LD by associating JSON-LD concepts such as <code>@subject</code>
      and <code>@type</code> with the equivalent <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>s in RDF. Further information about
      RDF may be found in [<cite><a class="bibref" rel="biblioentry" href="#bib-RDF-PRIMER">RDF-PRIMER</a></cite>].</p>

    <p>Some examples of encoding <a class="tref internalDFN" title="rdf" href="#dfn-rdf">RDF</a> into JSON-LD may be found
      in <a href="#markup-examples">Appendix A</a>. Details of transforming JSON-LD into RDF
      are defined in [<cite><a class="bibref" rel="biblioentry" href="#bib-JSON-LD-API">JSON-LD-API</a></cite>].</p>
  </div>

  <div class="appendix section" id="markup-examples">

  <!-- OddPage -->
  <h2><span class="secno">A. </span>Markup Examples</h2>

  <p>The JSON-LD markup examples below demonstrate how JSON-LD can be used to
    express semantic data marked up in other languages such as RDFa, Microformats,
    and Microdata. These sections are merely provided as proof that JSON-LD is
    very flexible in what it can express across different <a class="tref internalDFN" title="linked_data" href="#dfn-linked_data">Linked Data</a> approaches.</p>

  <div id="turtle" class="section">
    <h3><span class="secno">A.1 </span>Turtle</h3>

    <p>The following are examples of representing <a class="tref internalDFN" title="rdf" href="#dfn-rdf">RDF</a> as expressed in [<cite><a class="bibref" rel="biblioentry" href="#bib-TURTLE">TURTLE</a></cite>] into JSON-LD.</p>

  <div id="prefix-and-base-definitions" class="section">
  <h4><span class="secno">A.1.1 </span>Prefix and Base definitions</h4>
  <p>The JSON-LD context has direct equivalents for Turtle <code>@base</code> and <code>@prefix</code> expressions:</p>

  <pre class="example">@base &lt;http://manu.sporny.org/&gt; .
  @prefix foaf: &lt;http://xmlns.com/foaf/0.1/&gt; .

  &lt;#me&gt; a foaf:Person;
    foaf:name &quot;Manu Sporny&quot;;
    foaf:homepage &lt;&gt; .</pre>

  <pre class="example">{
    &quot;@context&quot;: {
      &quot;@base&quot;:  &quot;http://manu.sporny.org/&quot;,
      &quot;foaf&quot;:   &quot;http://xmlns.com/foaf/0.1/&quot;
    },
    &quot;@subject&quot;:       &quot;#me&quot;,
    &quot;@type&quot;:          &quot;foaf:Person&quot;,
    &quot;foaf:name&quot;:      &quot;Manu Sporny&quot;,
    &quot;foaf:homepage&quot;:  {&quot;@iri&quot;: &quot;&quot;}
  }</pre>
  </div>

  <div id="chaining-1" class="section">
  <h4><span class="secno">A.1.2 </span>Chaining</h4>
  <p>Both Turtle and JSON-LD allow chaining of objects, although Turtle only allows chaining of objects which
    use nlank node identifiers.</p>
  </div>

  <pre class="example">@base &lt;http://manu.sporny.org/&gt; .
  @prefix foaf: &lt;http://xmlns.com/foaf/0.1/&gt; .

  &lt;#me&gt; a foaf:Person;
    foaf:name &quot;Manu Sporny&quot;;
    foaf:knows [ a foaf:Person; foaf:name &quot;Gregg Kellogg&quot; ] .</pre>

  <pre class="example">{
    &quot;@context&quot;: {
      &quot;@base&quot;:  &quot;http://manu.sporny.org/&quot;,
      &quot;foaf&quot;:   &quot;http://xmlns.com/foaf/0.1/&quot;
    },
    &quot;@subject&quot;:       &quot;#me&quot;,
    &quot;@type&quot;:          &quot;foaf:Person&quot;,
    &quot;foaf:name&quot;:      &quot;Manu Sporny&quot;,
    &quot;foaf:knows&quot;:  {
      &quot;@type&quot;:          &quot;foaf:Person&quot;,
      &quot;foaf:name&quot;:      &quot;Gregg Kellogg&quot;
    }
  }</pre>
  <div id="lists-1" class="section">
  <h4><span class="secno">A.1.3 </span>Lists</h4>
  <p>Both JSON-LD and Turtle can represent sequential lists of values.</p>

  <pre class="example">@prefix foaf: &lt;http://xmlns.com/foaf/0.1/&gt; .

  &lt;http://example.org/people#joebob&gt; a foaf:Person;
    foaf:name &quot;Joe Bob&quot;;
    foaf:nick ( &quot;joe&quot; &quot;bob&quot; &quot;jaybee&quot;) .</pre>

  <pre class="example">{
    &quot;@context&quot;: {
      &quot;@base&quot;:  &quot;http://manu.sporny.org/&quot;,
      &quot;foaf&quot;:   &quot;http://xmlns.com/foaf/0.1/&quot;
    },
    &quot;@subject&quot;:       &quot;http://example.org/people#joebob&quot;,
    &quot;@type&quot;:          &quot;foaf:Person&quot;,
    &quot;foaf:name&quot;:      &quot;Joe Bob&quot;,
    &quot;foaf:nick&quot;:      {&quot;@list&quot;: [&quot;joe&quot;, &quot;bob&quot;, &quot;jaybe&quot;]}
  }</pre>
  </div>

  </div>

  <div id="rdfa" class="section">
  <h3><span class="secno">A.2 </span>RDFa</h3>

  <p>The following example describes three people with their respective names and
  homepages.</p>

  <pre class="example">&lt;div <span class="diff">prefix=&quot;foaf: http://xmlns.com/foaf/0.1/&quot;</span>&gt;
     &lt;ul&gt;
        &lt;li <span class="diff">typeof=&quot;foaf:Person&quot;</span>&gt;
          &lt;a <span class="diff">rel=&quot;foaf:homepage&quot; href=&quot;http://example.com/bob/&quot; property=&quot;foaf:name&quot; </span>&gt;Bob&lt;/a&gt;
        &lt;/li&gt;
        &lt;li <span class="diff">typeof=&quot;foaf:Person&quot;</span>&gt;
          &lt;a <span class="diff">rel=&quot;foaf:homepage&quot; href=&quot;http://example.com/eve/&quot; property=&quot;foaf:name&quot; </span>&gt;Eve&lt;/a&gt;
        &lt;/li&gt;
        &lt;li <span class="diff">typeof=&quot;foaf:Person&quot;</span>&gt;
          &lt;a <span class="diff">rel=&quot;foaf:homepage&quot; href=&quot;http://example.com/manu/&quot; property=&quot;foaf:name&quot; </span>&gt;Manu&lt;/a&gt;
        &lt;/li&gt;
     &lt;/ul&gt;
  &lt;/div&gt;</pre>

  <p>An example JSON-LD implementation is described below, however, there are
  other ways to mark-up this information such that the <a class="tref internalDFN" title="context" href="#dfn-context">context</a> is not
  repeated.</p>

  <pre class="example">{
    &quot;@context&quot;: { &quot;foaf&quot;: &quot;http://xmlns.com/foaf/0.1/&quot;},
    &quot;@subject&quot;: [
     {
       &quot;@subject&quot;: &quot;_:bnode1&quot;,
       &quot;@type&quot;: &quot;foaf:Person&quot;,
       &quot;foaf:homepage&quot;: &quot;http://example.com/bob/&quot;,
       &quot;foaf:name&quot;: &quot;Bob&quot;
     },
     {
       &quot;@subject&quot;: &quot;_:bnode2&quot;,
       &quot;@type&quot;: &quot;foaf:Person&quot;,
       &quot;foaf:homepage&quot;: &quot;http://example.com/eve/&quot;,
       &quot;foaf:name&quot;: &quot;Eve&quot;
     },
     {
       &quot;@subject&quot;: &quot;_:bnode3&quot;,
       &quot;@type&quot;: &quot;foaf:Person&quot;,
       &quot;foaf:homepage&quot;: &quot;http://example.com/manu/&quot;,
       &quot;foaf:name&quot;: &quot;Manu&quot;
     }
    ]
  }</pre>

  </div>

  <div id="microformats" class="section">
  <h3><span class="secno">A.3 </span>Microformats</h3>

  <p>The following example uses a simple Microformats hCard example to express
  how the Microformat is represented in JSON-LD.</p>

  <pre class="example">&lt;div class=&quot;vcard&quot;&gt;
   &lt;a class=&quot;url fn&quot; href=&quot;http://tantek.com/&quot;&gt;Tantek Çelik&lt;/a&gt;
  &lt;/div&gt;</pre>

  <p>The representation of the hCard expresses the Microformat terms in the
  <a class="tref internalDFN" title="context" href="#dfn-context">context</a> and uses them directly for the <code>url</code> and <code>fn</code>
  properties. Also note that the Microformat to JSON-LD processor has
  generated the proper URL type for <code>http://tantek.com</code>.</p>

  <pre class="example">{
    &quot;@context&quot;:
    {
      &quot;vcard&quot;: &quot;http://microformats.org/profile/hcard#vcard&quot;,
      &quot;url&quot;: &quot;http://microformats.org/profile/hcard#url&quot;,
      &quot;fn&quot;: &quot;http://microformats.org/profile/hcard#fn&quot;,
      &quot;@coerce&quot;: { &quot;@iri&quot;: &quot;url&quot; }
    },
    &quot;@subject&quot;: &quot;_:bnode1&quot;,
    &quot;@type&quot;: &quot;vcard&quot;,
    &quot;url&quot;: &quot;http://tantek.com/&quot;,
    &quot;fn&quot;: &quot;Tantek Çelik&quot;
  }</pre>

  </div>

  <div id="microdata" class="section">
  <h3><span class="secno">A.4 </span>Microdata</h3>

  <p>The Microdata example below expresses book information as a Microdata Work
  item.
  </p>

  <pre class="example">&lt;dl itemscope
      itemtype=&quot;http://purl.org/vocab/frbr/core#Work&quot;
      itemid=&quot;http://purl.oreilly.com/works/45U8QJGZSQKDH8N&quot;&gt;
   &lt;dt&gt;Title&lt;/dt&gt;
   &lt;dd&gt;&lt;cite itemprop=&quot;http://purl.org/dc/terms/title&quot;&gt;Just a Geek&lt;/cite&gt;&lt;/dd&gt;
   &lt;dt&gt;By&lt;/dt&gt;
   &lt;dd&gt;&lt;span itemprop=&quot;http://purl.org/dc/terms/creator&quot;&gt;Wil Wheaton&lt;/span&gt;&lt;/dd&gt;
   &lt;dt&gt;Format&lt;/dt&gt;
   &lt;dd itemprop=&quot;http://purl.org/vocab/frbr/core#realization&quot;
       itemscope
       itemtype=&quot;http://purl.org/vocab/frbr/core#Expression&quot;
       itemid=&quot;http://purl.oreilly.com/products/9780596007683.BOOK&quot;&gt;
    &lt;link itemprop=&quot;http://purl.org/dc/terms/type&quot; href=&quot;http://purl.oreilly.com/product-types/BOOK&quot;&gt;
    Print
   &lt;/dd&gt;
   &lt;dd itemprop=&quot;http://purl.org/vocab/frbr/core#realization&quot;
       itemscope
       itemtype=&quot;http://purl.org/vocab/frbr/core#Expression&quot;
       itemid=&quot;http://purl.oreilly.com/products/9780596802189.EBOOK&quot;&gt;
    &lt;link itemprop=&quot;http://purl.org/dc/terms/type&quot; href=&quot;http://purl.oreilly.com/product-types/EBOOK&quot;&gt;
    Ebook
   &lt;/dd&gt;
  &lt;/dl&gt;</pre>

  <p>Note that the JSON-LD representation of the Microdata information stays
  true to the desires of the Microdata community to avoid contexts and
  instead refer to items by their full <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>.</p>

  <pre class="example">[
    {
      &quot;@subject&quot;: &quot;http://purl.oreilly.com/works/45U8QJGZSQKDH8N&quot;,
      &quot;@type&quot;: &quot;http://purl.org/vocab/frbr/core#Work&quot;,
      &quot;http://purl.org/dc/terms/title&quot;: &quot;Just a Geek&quot;,
      &quot;http://purl.org/dc/terms/creator&quot;: &quot;Whil Wheaton&quot;,
      &quot;http://purl.org/vocab/frbr/core#realization&quot;:
        [&quot;http://purl.oreilly.com/products/9780596007683.BOOK&quot;, &quot;http://purl.oreilly.com/products/9780596802189.EBOOK&quot;]
    },
    {
      &quot;@subject&quot;: &quot;http://purl.oreilly.com/products/9780596007683.BOOK&quot;,
      &quot;@type&quot;: &quot;http://purl.org/vocab/frbr/core#Expression&quot;,
      &quot;http://purl.org/dc/terms/type&quot;: &quot;http://purl.oreilly.com/product-types/BOOK&quot;
    },
    {
      &quot;@subject&quot;: &quot;http://purl.oreilly.com/products/9780596802189.EBOOK&quot;,
      &quot;@type&quot;: &quot;http://purl.org/vocab/frbr/core#Expression&quot;,
      &quot;http://purl.org/dc/terms/type&quot;: &quot;http://purl.oreilly.com/product-types/EBOOK&quot;
    }
  ]</pre>
  </div>
  </div>

  <div class="appendix section" id="mashing-up-vocabularies">

  <!-- OddPage -->
  <h2><span class="secno">B. </span>Mashing Up Vocabularies</h2>

  <p>Developers would also benefit by allowing other vocabularies to be used
  automatically with their JSON API. There are over 200
  <a class="tref internalDFN" title="web_vocabulary" href="#dfn-web_vocabulary">Web Vocabulary</a> Documents that are available for use on the Web
  today. Some of these vocabularies are:
  </p>

  <ul>
     <li>RDF - for describing information about objects and concepts on the Web.</li>
     <li>RDFS - for expressing things like labels and comments.</li>
     <li>XSD - for specifying basic types like strings, integers, dates and times.</li>
     <li>Dublin Core - for describing creative works.</li>
     <li>FOAF - for describing social networks.</li>
     <li>Calendar - for specifying events.</li>
     <li>SIOC - for describing discussions on blogs and websites.</li>
     <li>CCrel - for describing Creative Commons and other types of licenses.</li>
     <li>GEO - for describing geographic location.</li>
     <li>VCard - for describing organizations and people.</li>
     <li>DOAP - for describing projects.</li>
  </ul>

  <p>You can use these vocabularies in combination, like so:</p>

  <pre class="example">{
    &quot;<span class="diff">@type</span>&quot;: &quot;<span class="diff">foaf:Person</span>&quot;,
    &quot;<span class="diff">foaf:name</span>&quot;: &quot;Manu Sporny&quot;,
    &quot;<span class="diff">foaf:homepage</span>&quot;: &quot;http://manu.sporny.org/&quot;,
    &quot;<span class="diff">sioc:avatar</span>&quot;: &quot;http://twitter.com/account/profile_image/manusporny&quot;
  }</pre>

  <p>Developers can also specify their own Vocabulary documents by modifying the
  <a class="tref internalDFN" title="active_context" href="#dfn-active_context">active context</a> in-line using the <code>@context</code> keyword,
  like so:</p>

  <pre class="example">{
    <span class="diff">&quot;@context&quot;: { &quot;myvocab&quot;: &quot;http://example.org/myvocab#&quot; }</span>,
    &quot;@type&quot;: &quot;foaf:Person&quot;,
    &quot;foaf:name&quot;: &quot;Manu Sporny&quot;,
    &quot;foaf:homepage&quot;: &quot;http://manu.sporny.org/&quot;,
    &quot;sioc:avatar&quot;: &quot;http://twitter.com/account/profile_image/manusporny&quot;<span class="diff">,
    &quot;myvocab:personality&quot;: &quot;friendly&quot;</span>
  }</pre>

  <p>The <code>@context</code> keyword is used to change how the JSON-LD
  processor evaluates key-value pairs. In this case, it was used to
  map one string ('myvocab') to another string, which is interpreted as
  a <a class="tref internalDFN" title="iri" href="#dfn-iri">IRI</a>. In the example above, the <code>myvocab</code> string is replaced
  with &quot;<code>http://example.org/myvocab#</code>&quot; when it
  is detected. In the example above, &quot;<code>myvocab:personality</code>&quot; would
  expand to &quot;<code>http://example.org/myvocab#personality</code>&quot;.</p>

  <p>This mechanism is a short-hand, called a <a class="tref internalDFN" title="web_vocabulary" href="#dfn-web_vocabulary">Web Vocabulary</a> <a class="tref internalDFN" title="prefix" href="#dfn-prefix">prefix</a>,
  and provides developers an unambiguous way to map any JSON value to RDF.</p><p>

  </p></div>

  <div class="appendix section" id="iana-considerations">

  <!-- OddPage -->
  <h2><span class="secno">C. </span>IANA Considerations</h2>

  <p>This section is included merely for standards community review and will be
  submitted to the Internet Engineering Steering Group if this specification
  becomes a W3C Recommendation.</p>

  <dl>
    <dt>Type name:</dt>
    <dd>application</dd>
    <dt>Subtype name:</dt>
    <dd>ld+json</dd>
    <dt>Required parameters:</dt>
    <dd>None</dd>
    <dt>Optional parameters:</dt>
    <dd>
      <dl>
        <dt><code>form</code></dt>
        <dd>Determines the serialization form for the JSON-LD document. Valid
          values include; <code>compacted</code>, <code>expanded</code>,
          <code>framed</code>, and <code>normalized</code>. Other values are
          allowed, but must be pre-pended with a <code>x-</code> string until
          they are clearly defined by a stable specification. If no form
          is specified in an HTTP request header to a responding application,
          such as a Web server, the application <em class="rfc2119" title="may">may</em> choose any form. If no
          form is specified for a receiving application, the form <em class="rfc2119" title="must not">must not</em>
          be assumed to take any particular form.</dd>
        <div class="issue">It is currently <a href="https://github.com/json-ld/json-ld.org/issues/14"> being discussed to remove form=framed</a> from this specification as there are several issues with it.</div>
      </dl>
    </dd>
    <dt>Encoding considerations:</dt>
    <dd>The same as the <code>application/json</code> MIME media type.</dd>
    <dt>Security considerations:</dt>
    <dd>Since JSON-LD is intended to be a pure data exchange format for
      directed graphs, the serialization <em class="rfc2119" title="should not">should not</em> be passed through a
      code execution mechanism such as JavaScript's <code>eval()</code>
      function. It is <em class="rfc2119" title="recommended">recommended</em> that a conforming parser does not attempt to
      directly evaluate the JSON-LD serialization and instead purely parse the
      input into a language-native data structure. </dd>
    <dt>Interoperability considerations:</dt>
    <dd>Not Applicable</dd>
    <dt>Published specification:</dt>
    <dd>The <a href="http://json-ld/spec/latest/">JSON-LD</a> specification.</dd>
    <dt>Applications that use this media type:</dt>
    <dd>Any programming environment that requires the exchange of
      directed graphs. Implementations of JSON-LD have been created for
      JavaScript, Python, Ruby, PHP and C++.
    </dd>
    <dt>Additional information:</dt>
    <dd>
      <dl>
        <dt>Magic number(s):</dt>
        <dd>Not Applicable</dd>
        <dt>File extension(s):</dt>
        <dd>.jsonld</dd>
        <dt>Macintosh file type code(s):</dt>
        <dd>TEXT</dd>
      </dl>
    </dd>
    <dt>Person &amp; email address to contact for further information:</dt>
    <dd>Manu Sporny &lt;msporny@digitalbazaar.com&gt;</dd>
    <dt>Intended usage:</dt>
    <dd>Common</dd>
    <dt>Restrictions on usage:</dt>
    <dd>None</dd>
    <dt>Author(s):</dt>
    <dd>Manu Sporny, Gregg Kellogg, Dave Longley</dd>
    <dt>Change controller:</dt>
    <dd>W3C</dd>
  </dl>

  </div>

  <div class="appendix section" id="acknowledgements">

  <!-- OddPage -->
  <h2><span class="secno">D. </span>Acknowledgements</h2>

  <p>The editors would like to thank Mark Birbeck, who provided a great deal of
  the initial push behind the JSON-LD work via his work on RDFj,
  Dave Longley, Dave Lehn and Mike Johnson who reviewed, provided feedback, and
  performed several implementations of the specification, and Ian Davis, who
  created RDF/JSON. Thanks also to Nathan Rixham, Bradley P. Allen,
  Kingsley Idehen, Glenn McDonald, Alexandre Passant, Danny Ayers, Ted
  Thibodeau Jr., Olivier Grisel, Niklas Lindström, Markus Lanthaler, and Richard
  Cyganiak for their input on the specification.
  </p>
  </div>



  <div id="references" class="appendix section">
  <!-- OddPage -->
  <h2><span class="secno">E. </span>References</h2><div id="normative-references" class="section"><h3><span class="secno">E.1 </span>Normative references</h3><dl class="bibliography"><dt id="bib-BCP47">[BCP47]</dt><dd>A. Phillips, M. Davis. <a href="http://tools.ietf.org/rfc/bcp/bcp47.txt"><cite>Tags for Identifying Languages</cite></a> September 2009. IETF Best Current Practice. URL: <a href="http://tools.ietf.org/rfc/bcp/bcp47.txt">http://tools.ietf.org/rfc/bcp/bcp47.txt</a>
  </dd><dt id="bib-RDF-CONCEPTS">[RDF-CONCEPTS]</dt><dd>Graham Klyne; Jeremy J. Carroll. <a href="http://www.w3.org/TR/2004/REC-rdf-concepts-20040210"><cite>Resource Description Framework (RDF): Concepts and Abstract Syntax.</cite></a> 10 February 2004. W3C Recommendation. URL: <a href="http://www.w3.org/TR/2004/REC-rdf-concepts-20040210">http://www.w3.org/TR/2004/REC-rdf-concepts-20040210</a> 
  </dd><dt id="bib-RFC3987">[RFC3987]</dt><dd>M. Dürst; M. Suignard. <a href="http://www.ietf.org/rfc/rfc3987.txt"><cite>Internationalized Resource Identifiers (IRIs).</cite></a> January 2005. Internet RFC 3987. URL: <a href="http://www.ietf.org/rfc/rfc3987.txt">http://www.ietf.org/rfc/rfc3987.txt</a> 
  </dd><dt id="bib-RFC4627">[RFC4627]</dt><dd>D. Crockford. <a href="http://www.ietf.org/rfc/rfc4627.txt"><cite>The application/json Media Type for JavaScript Object Notation (JSON)</cite></a> July 2006. Internet RFC 4627. URL: <a href="http://www.ietf.org/rfc/rfc4627.txt">http://www.ietf.org/rfc/rfc4627.txt</a>
  </dd><dt id="bib-WEBIDL">[WEBIDL]</dt><dd>Cameron McCormack. <a href="http://www.w3.org/TR/2008/WD-WebIDL-20081219"><cite>Web IDL.</cite></a> 19 December 2008. W3C Working Draft. (Work in progress.) URL: <a href="http://www.w3.org/TR/2008/WD-WebIDL-20081219">http://www.w3.org/TR/2008/WD-WebIDL-20081219</a> 
  </dd></dl></div><div id="informative-references" class="section"><h3><span class="secno">E.2 </span>Informative references</h3><dl class="bibliography"><dt id="bib-ECMA-262">[ECMA-262]</dt><dd><a href="http://www.ecma-international.org/publications/standards/Ecma-262.htm"><cite>ECMAScript Language Specification, Third Edition.</cite></a> December 1999. URL: <a href="http://www.ecma-international.org/publications/standards/Ecma-262.htm">http://www.ecma-international.org/publications/standards/Ecma-262.htm</a> 
  </dd><dt id="bib-HTML-RDFA">[HTML-RDFA]</dt><dd>Manu Sporny; et al. <a href="http://www.w3.org/TR/rdfa-in-html/"><cite>HTML+RDFa</cite></a> 04 March 2010. W3C Working Draft. URL: <a href="http://www.w3.org/TR/rdfa-in-html/">http://www.w3.org/TR/rdfa-in-html/</a> 
  </dd><dt id="bib-JSON-LD-API">[JSON-LD-API]</dt><dd>Manu Sporny, Gregg Kellogg, Dave Longley, Eds. <cite><a href="http://json-ld.org/spec/latest/json-ld-api/">JSON-LD API</a></cite> Latest. W3C Editor's Draft. URL: <a href="http://json-ld.org/spec/latest/json-ld-api/">http://www.w3.org/2010/02/rdfa/sources/rdf-interfaces/</a>
  </dd><dt id="bib-MICRODATA">[MICRODATA]</dt><dd>Ian Hickson; et al. <a href="http://www.w3.org/TR/microdata/"><cite>Microdata</cite></a> 04 March 2010. W3C Working Draft. URL: <a href="http://www.w3.org/TR/microdata/">http://www.w3.org/TR/microdata/</a> 
  </dd><dt id="bib-MICROFORMATS">[MICROFORMATS]</dt><dd><a href="http://microformats.org"><cite>Microformats</cite></a>. URL: <a href="http://microformats.org">http://microformats.org</a> 
  </dd><dt id="bib-RDF-PRIMER">[RDF-PRIMER]</dt><dd>Frank Manola; Eric Miller. <a href="http://www.w3.org/TR/2004/REC-rdf-primer-20040210/"><cite>RDF Primer.</cite></a> 10 February 2004. W3C Recommendation. URL: <a href="http://www.w3.org/TR/2004/REC-rdf-primer-20040210/">http://www.w3.org/TR/2004/REC-rdf-primer-20040210/</a> 
  </dd><dt id="bib-RDF-SCHEMA">[RDF-SCHEMA]</dt><dd>Dan Brickley; Ramanathan V. Guha. <a href="http://www.w3.org/TR/2004/REC-rdf-schema-20040210"><cite>RDF Vocabulary Description Language 1.0: RDF Schema.</cite></a> 10 February 2004. W3C Recommendation. URL: <a href="http://www.w3.org/TR/2004/REC-rdf-schema-20040210">http://www.w3.org/TR/2004/REC-rdf-schema-20040210</a> 
  </dd><dt id="bib-RDFA-CORE">[RDFA-CORE]</dt><dd>Shane McCarron; et al. <a href="http://www.w3.org/TR/2011/WD-rdfa-core-20110331"><cite>RDFa Core 1.1: Syntax and processing rules for embedding RDF through attributes.</cite></a> 31 March 2011. W3C Working Draft. URL: <a href="http://www.w3.org/TR/2011/WD-rdfa-core-20110331">http://www.w3.org/TR/2011/WD-rdfa-core-20110331</a> 
  </dd><dt id="bib-RFC3986">[RFC3986]</dt><dd>T. Berners-Lee; R. Fielding; L. Masinter. <a href="http://www.ietf.org/rfc/rfc3986.txt"><cite>Uniform Resource Identifier (URI): Generic Syntax.</cite></a> January 2005. Internet RFC 3986. URL: <a href="http://www.ietf.org/rfc/rfc3986.txt">http://www.ietf.org/rfc/rfc3986.txt</a> 
  </dd><dt id="bib-TURTLE">[TURTLE]</dt><dd>David Beckett, Tim Berners-Lee. <a href="http://www.w3.org/TeamSubmission/turtle/"><cite>Turtle: Terse RDF Triple Language.</cite></a> January 2008. W3C Team Submission. URL: <a href="http://www.w3.org/TeamSubmission/turtle/">http://www.w3.org/TeamSubmission/turtle/</a> 
  </dd></dl></div></div></body></html>2011. W3C Working Draft. URL: <a href="http://www.w3.org/TR/2011/WD-rdfa-core-20110331">http://www.w3.org/TR/2011/WD-rdfa-core-20110331</a> 
</dd><dt id="bib-RFC3986">[RFC3986]</dt><dd>T. Berners-Lee; R. Fielding; L. Masinter. <a href="http://www.ietf.org/rfc/rfc3986.txt"><cite>Uniform Resource Identifier (URI): Generic Syntax.</cite></a> January 2005. Internet RFC 3986. URL: <a href="http://www.ietf.org/rfc/rfc3986.txt">http://www.ietf.org/rfc/rfc3986.txt</a> 
</dd><dt id="bib-TURTLE">[TURTLE]</dt><dd>David Beckett, Tim Berners-Lee. <a href="http://www.w3.org/TeamSubmission/turtle/"><cite>Turtle: Terse RDF Triple Language.</cite></a> January 2008. W3C Team Submission. URL: <a href="http://www.w3.org/TeamSubmission/turtle/">http://www.w3.org/TeamSubmission/turtle/</a> 
</dd></dl></div></div></body></html>